XIX.—PAL.EO-GEOLOGICAL AND GEOGEAPHICAL MAPS OF THE BEITISH ISLANDS AND THE ADJOINING PAETS OF THE CONTINENT OF EUEOPE. By Edward Hull, ll.d., f.r.s., &c., Director of the Geological Survey op Ireland, and Professor of Geology in the Eoyal College of Science, Dublin. Plates XXII. to XXXV. Introduction. The preparation of a series of maps showing the relations of land and sea during successive geological periods over the British area has been an undertaking which I have long contemplated, but, until now,, did not see my way to carry out. The idea has, doubtless, suggested itself to other geologists ; and I cannot but feel surprise that, except very partially, no one has hitherto made the attempt to realize it. I understand from the Eev. Dr. Haughton, of Trinity College, Dublin, that about a quarter of a century ago, the late Mr. William Longman, the then head of the eminent publishing firm, expressed a wish to have such a set of maps prepared for publication, and suggested that he (Dr. Haughton) should undertake their preparation. Circumstances prevented this ; but it may be affirmed with some confidence that the time had not then arrived when this task could have been accomplished with satisfactory results; because it is within this period that much of our present knowledge of the structure of, at least, the English area has been obtained by the details collected and portrayed on maps by the Government Surveyors, and by the numerous deep underground boring-experiments which have been made at intervals over a large portion of the centre or south of that country in search of either coal, water, or for other purposes. These borings have been of the greatest interest to geologists, though perhaps not always equally so to their projectors, because they have revealed the internal structure of a large extent of country which would otherwise have been the subject only of conjecture or of geological inference. For the present purpose they have proved of material use. Certainly, without their aid it would have been impossible for me to have shown accurately, the range of the Triassic, Liassic, and Oolitic formations in the direction of the Thames valley and of the eastern coast, after they had been successively lost sight of beneath the more recent deposits. These borings have also thrown much light upon the position of the Carboniferous, Devonian, and Silurian rocks below the Cretaceous area; and though they have not solved the question so ably handled on physical grounds by Murchison, Godwin-Austen, and Prestwich—“ Where may coal be found under the newer formations of the South of England,” they have to a very large extent shown where the TRANS. KOV. DUB. SOC., N.S., VOX.. I. 2 X 258 Palceo-Geological and Geographical Maps of the British Islands. coal-formation does not exist, and what kinds of strata occupy its place. Now, nearly all the borings which have thrown any light on the internal structure of sub-Jurassic or sub-Cretaceous areas have been made within the last quarter of a century; and until they had been made, geologists were not in a position to deal with any degree of certainty with the problems I have referred to, much less to represent their views on physiographical maps. In tracing out the range of special formations over tracts of country of considerable extent and noting the changes they undergo, the mind is naturally led to speculate on their original extent and distribution before they had undergone the denudation or waste, to which they have subsequently been exposed. The formations of the British Isles and of the adjoining parts of the European continent are only fragments of the original masses; they have been disturbed from their once horizontal position, tilted into various angular inclinations from the horizon, and have undergone much waste, so that we seldom meet with the original “ shore beds ” which were deposited in the waters of the sea or lake (as the case may be), along the margins of their hydrographical areas. Hence we are led on to speculate regarding the position of the old lands which yielded the sediment of which the strata are formed, or which bounded their areas of deposition. In order to arrive at conclusions on these subjects, we have to note the directions in which these special formations expand in thickness, and those towards which they appear to thin away. Generally speaking, and within certain limits, formations composed of sedimentary materials, such as gravel, sand, clay or mud, tend to increase in thickness in the direction of the land from which these materials were carried down and spread over the area of deposition. On the other hand, formations of this kind rapidly thin away in the direction of any tract of contemporaneous land, against the shelving bod or shore of which they were deposited, but which may not itself have contributed much, if any, sediment during their deposition. The old ridge of Lower Palaeozoic rocks which stretched across the centre of England during the Carboniferous and Permian periods was of this kind.* Itself of too limited an extent to be a source of sediment, the newer formations simply tail out towards its margin both to the north and to the south. The sub-Cretaceous ridge of a subsequent period was of a similar kind.t While it formed a land-surface against which the Triassic and Jurassic formations successively wedged out, it was not itself a source of sediment, and these formations terminate along its border, but little changed in their mineral characters on approaching its position. On the other hand, limestones formed over the bed of the sea by organic agency, become split up by bands of sandstone or shale in the direction of the lands of the period from which sandy or muddy sediment was being carried down by streams; but on approaching barriers of land, or isolated tracts of older rock of limited extent, they wedge out towards • Plate XXVIII., Fig. 2. t Plate XXXI., Figs. 1 & 2. 259 Palceo-Geological and Geographical Maps of the British Islands. the margin without much change in their characters ; of these two phenomena the Carbonilerous and Jurassic limestones offer striking examples.* In determining the position of the land surfaces, and submerged areas during successive geological periods, one of the most important guides is the discordant, or unconformable, relations of the strata to those of older date. Where two sets of strata, such as those of the Triassic and Silurian periods, are highly discordant to one another, there is much probability that the older formation was in some region in the position of a land surface when the newer formation was being deposited under the waters of an adjoining sea or lake. In this case the actual margin is frequently indicated by the abrupt uprising of the older formation with reference to the newer, allowance being in all cases made for the effects of denudation. If the two unconformable sets of strata immediately succeed each other, or are in close geological sequence, then the marginal relations are more easy of determination. Such is the case, for instance, with the Lower and Upper Silurian strata, which, though highly discordant as regards stratification, are in immediate geological sequence, and the original marginal beds, those of the upper Llandovery age, are found in the form of conglomerates not far removed from their position as shore beds.f Throughout the whole succession of formations from the Cambrian to the Cretaceous there is no more marked physical break than that which occurs between the Lower and Upper Silurian formations over the area of the British Islands. The occurrence of beds of conglomerate, or breccia, is generally an indication of littoral conditions, and indicates the proximity of the land of the period to which they belong. Thus, the breccias which occur in the New Red Sandstone in two stratigraphical positions in Shropshire and Worcestershire, and which thin away eastward, indicate the proximity of the marginal land formed of Devonian, Silurian, and Cambrian rocks, in the adjoining districts west of the Severn. The conglomerates of the Old Red Sandstone along the southern slopes of the Grampians, and in other places, point to similar conditions; but it is remarkable to how great a distance rounded pebbles have been transported in some instances from their original sources; as, for example, in the case of the New.Red Conglomerate of the central counties of England, the source of supply for which was apparently in Scotland.^ When engaged in the attempt to restore the physical features of successive geological periods over the region embraced in this treatise, I became forcibly impressed with two leading ideas. First, that the present North Atlantic Ocean, * Some years ago I illustrated tliese phenomena in a paper on “ Isodiametric lines, and the relative distribution of the calcareous and sedimentary beds of the Carboniferous system.”—Quart. Jour. Geol. Soc., vol. xviii., p. 127. t This can be observed both in Wales and the West of Ireland. + On the origin of the quartzite pebbles of the Bunter Conglomerate, see “ The Triassic and Permian Bocks of the Midland Counties of England,” p. 59.—Mem. Geol. Survey (1869). 260 Palceo-Geological and Geographical Maps of the British Islands. must for a long lapse of time have been a continental area, whence was derived to a large extent the sediment of which many of our formations are composed; and, secondly, that the Old Highland districts of the British Isles, once they had sprang into existence as such, ever after endeavoured to retain their ascendency.* This is the case with the mountains of North Wales, those of the Scottish Highlands, and of Donegal, Galway, and Wicklow, in Ireland, which all rose into mountain forms or elevated positions during that long interval of time which elapsed between the close of the Lower, and the commencement of the Upper Silurian epochs.! Notwithstanding the enormous amount of waste to which these old mountain groups have been subjected, it is doubtful if at any time subsequently they were completely buried beneath more recent strata. In several instances, however, this was nearly being the case ; as, for example, during the epochs of deep depression in the Upper Carboniferous and Cretaceous periods.^ The first idea above referred to is one of great interest, and seems to run counter to the prevalent theory, that the existing oceans have been such from very remote geological periods. If this were the case, the existing Continents must equally have been Continents throughout an equal distance of time; but, if so, how could they have been covered so largely by marine strata, belonging to Silurian, Devonian, Carboniferous, Jurassic, Cretaceous, and Eocene Tertiary times? The conclusion has been forced on my own mind, that the North Atlantic was mainly land during the Laurentian, Cambrian, and Lower Silurian periods, and was the source of the sediment of which these great formations are composed. It probably first assumed large proportions as a sea or ocean, when so much of the then sea became land, namely, at the close of the Lower Silurian period ; but there are grounds for believing that it was largely in the condition of a land surface in still later times, namely, during the Carboniferous, Permian, Triassic, and Jurassic periods, as evinced by the thickening of the sediment both towards the north-west and south-west of the British Isles.§ This great continent of Atlantis was the parent of much of the strata which now overspreads the plains of Britain and of the adjoining continental areas. With the Cretaceous period its permanently oceanic form and features set in, and were vastly extended during that and the succeeding period of the nummulitic limestone. * Prof. Sir A. Ramsay has shown that the mountains of North Wales became such before the Upper Silurian period, and it is doubtful if they were ever subsequently completely buried under strata of any newer formation.—See “ Phys. Geol. and Geog. of Gt. Britain,” 4th edit, t “ Phys. Geol. and Geog. of Ireland,” p. 123 et seq. (1879.) f See Maps, Plates XXVIII. and XXXII. §1 have shown this to have been the case with reference to the Carboniferous Bocks.—Quart. Journ., Geol. Soc., vol. xviii., p. 142, and of the Lower Secondary Rocks, Ibid., vol. xvi., p. 63 et seq. Palceo-Geological and Geographical Maps of the British Islands, 261 Plate XXII. The Laurentian Period. This plate (Fig. 1), is intended to show those tracts where the Laurentian rocks reach the surface, and those under which they may be supposed to extend, though concealed beneath more recent formations ; also, the portions of the surface oyer the western part of the European area, including the British Isles, occupied by the land and sea of the Laurentian, or Archaean, period (Fig. 2). The Laurentian Continent (Atlantis). —As the Laurentian rocks form extensive tracts both in North America and Europe, it may be inferred that the land which was the source of the sediment of which they are composed was situated in a region lying between these two areas; that is to say, in the region of the Atlantic Ocean, including probably the continent of Greenland, and possibly the Polar regions. It may be supposed that large rivers flowed down into the ocean of the period, both towards the west and towards the east, and that this sediment was deposited over the floor of the Laurentian ocean, now occupied by North America and Europe. The margins of this land are necessarily only approximately inferential. Laurentian Areas (Fig. 1).—The Laurentian (or pre-Cambrian) rocks appear at the surface (over the area embraced by the map), as forming the greater portion of the Scandinavian promontory, in the north-western Highlands of Scotland, and outer Hebrides, in the north-west of Ireland and Galway, in the centre and northwest of France, and along the margin of the Silurian basin of Bohemia. They may be supposed to underlie all the remaining portions of the land, except those districts formed of intrusive granitic or trappean rocks, which, as compared with the former areas, are very small, and can only occasionally be represented on a map of the scale here adopted. Nature of the Laurentian Pocks. —These rocks consist of foliated granite or gneiss, hornblendic and micaceous schists, crystalline limestone or marble. The gneiss is generally massive, porphyritic, and of a red colour, consisting of orthoclase, oligoclase, quartz, and mica of two varieties. To this formation, the red granite of the Nile valley probably belongs. The Laurentian rocks have undergone intense metamorphism, owing to which they now only occur in a crystalline condition. Originally, there is every reason to believe, they were formed of sedimentary materials, such as those of the Lower Silurian system, consisting of sandstones or grits, slates, flagstones, and limestones, all of marine origin; and whether or not the Eozoon Canadense, found in this formation in Canada, be a true organism, the occurrence of beds of limestone leads us to infer that the ocean-waters of this early period of geological history were not destitute of living creatures, though probably of very simple organization. -o- Palceo-Geological and Geographical Maps of the British Islands. Plate XXIII. The Cambrian Period. The physical conditions of the Cambrian period over the British area contrast strongly ivith those of the Laurentian. Previous to the deposition of the Cambrian beds,* those of the preceding Laurentian period had been metamorphosed, elevated into land-areas, and largely denuded, so that the bed of the Laurentian ocean (Plate XXII.) now appears as part of a large continental area, embracing the northern and western portions of the British Isles; while the ocean extended over the western districts of Europe, the whole of England, and parts of Scotland and Ireland. Submerged Cambrian areas. —From considerations stated at length elsewhere,t I have arrived at the conclusion, that during the Cambrian period, an archfean ridge formed of Laurentian strata stretched through the British Isles in a S. W. and N.E. direction, embracing the region of the west of Ireland, and of the Grampian Mountains, by which the Cambrian beds of the N.W. Highlands of Scotland were separated off from their representatives of the English and Welsh areas. This conclusion depends in part on the extreme dissimilarity existing between the representative beds on either side of the supposed ridge. I shall, therefore, describe the beds under the two types which I have called, on the occasion referred to, those of the “Caledonian,” and “ Hiberno-Cambrian.” Cambrian Beds of the Caledonian type. —These are restricted to the northwestern Highlands of Scotland, where they occur interposed between the Laurentian rocks below, and the quartzites, limestones, and shales of the Lower Silurian beds above. They consist of great beds of red and purple sandstone and conglomerate, generally in nearly horizontal positions, forming bold escarpments, and isolated pyramidal masses. The pebbles of which they are mainly formed consist of various kinds of gneiss, schist, porphyry, and quartzite;—presumably derived from the adjoining land-areas of Laurentian strata. Professor Ramsay considers these beds to have been deposited in the waters of an inland lake, of which the outer Hebrides formed the western margin.! In this view I concur. No fossils have been found in these Jacustrine beds. Cambran Beds of the Hibernu- Cambrian type. —These are vastly more extensive than the former ; and, though they only crop out to the surface in a few places, may be presumed to underlie nearly the whole of England and Wales, as well as the adjoining parts of Europe. They consist of green and purple massive grits, quartz rocks and slates, with, occasionally, pebbly beds; and as the fauna is distinctly marine the * I use the term Cambrian to include the Longmynd, Harlech, and Llanberis beds, together with the overlying Upper Cambrian Lingula flags, as the fauna of the latter has been shown by Dr. Hicks to be present in the former. I therefore take the base of the Silurian series at the Tremadoc slates. t “Quart. Joum., Geol. Soc.,” May, 1882, p. 210, and Brit. Assoc. Rep. (1881, p. 642.) I “ Phys. Geology and Geography of Great Britain," 5 edit., 283, &c. 263 Palceo-Geological and Geographical Maps of the British Islands. beds may be inferred to be of oceanic origin. Cambrian rocks of this type are found in the east of Ireland, with Oldhamia, a sertularian zoophyte, and annelid tracks and borings, such as those of Histioderma. In North Wales and Shropshire they have yielded trilobites,* * * § while the Upper Cambrian beds are rich in marine forms. At St. David’s, Dr. Hicks has brought to light several genera of trilobites in beds contemporaneous with those of the Longmynd and Harlech group of North Wales. These rocks also are found in Cliarnwood Forest, in Leicestershire,! where they are in some places altered or metamorphosed, and associated with trap rocks; in the Ardennes mountains, on the borders of France and Belgium, where they consist of quartzites, quartz-schists, and schists, with Oldhamia radiata (one of the Irish species), Dictyonema sociale, Lingula, and tubes or impressions of annelids. J In the Systeme Salmien, forming the upper division of the series, trilobites of the genus Paradoxides have been discovered by M. Malaise.§ These rocks also occur in Normandy and Brittany, consisting of green slates and grits, resting on gneiss and schist, which is probably of Laurentian age. Regarded as a whole, the Cambrian beds of the region now described are clearly of marine origin, and present—both in lithological characters, and from the occurrence of a marine fauna—a marked dissimilarity to the beds of the Caledonian type. Plate XXIY. The Loiver Silurian Period. With the commencement of the Lower Silurian period,|| the ocean resumed the dominion it had partially lost during the preceding Cambrian period ; and as time went on, the entire area of the British Islands and adjoining parts of Europe became submerged and covered with sediment. It may be confidently affirmed, that there is not a square mile over this region which was not originally buried beneath strata belonging to the Lower Silurian period. The old arclisean ridge was covered by strata still in existence; and even the Cambrian and Laurentian rocks of the north Highlands of Scotland were, in the opinion of Sir A. C. Ramsay, submerged and buried under the accumulating piles of these strata before that era passed away.I' Land was, however, probably not far away, and its position was to the north-west of the British Isles. * Discovered by Mr. Salter in the Longmynd beds. 11 regret I cannot agree with Dr. Hicks and several other distinguished geologists in regarding these beds otherwise than of Cambrian age, to which they were originally referred by Professor Jukes. JDr. Mourlon, t! Geologic de la Belgique,” t. 1., p. 31. § Dalimier, Bull. Soc. Geol. France, 2 Ser., vol. xx. || I assume the base of the Lower Silurian series to be the Tremadoc slate or (in their absence) the .Arenig beds, forming the lower part of the Llandeilo group. 11 “ Phys. Geog. and Geol. of Great Britain,” 5 edit., p. 87. 264 Palceo-Geological and Geographical Maps of the British Islands. Nature of the Lower Silurian Beds. —The strata of this period consist of dark and gray slates, grits sometimes calcareous, and, rarely, bands of limestone. The fossils are all of marine genera. Over the northern and western areas of the British Isles these strata have undergone extensive metamorphism, so that in the Highlands of Scotland, and of the north and west of Ireland, they consist of quartzites, micaceous, talcose, and chloritic schists, and crystalline limestones, sometimes serpentinous, with their varieties; presenting a marked contrast to their unaltered representatives in the south of Scotland, in Wales, and in the east of Ireland. Relations to adjoining Formations. —The Lower Silurian rocks are discordantly superimposed upon all formations older than themselves. This is the case in North Wales, in the east of Ireland, and in the north of Scotland Owing to this discordancy, and the large amount of denudation to which the upper and lower Cambrian beds were subjected at the close of the Cambrian period, we find the Lower Silurian beds resting on strata of various stratigraphical positions. Thus in North Wales and Salop, the Arenig beds are found resting sometimes (as near Bangor and Carnarvon) on the purple slates and conglomerates of the Cambrian series ;* sometimes, as in Pembrokeshire and Merionethshire, on the Tremadoc slates. In the east of Ireland in county Wicklow, the Lower Silurian beds rest discordantly on the Lower Cambrian beds; and in the north of Scotland, the quartzites and limestones representing the Llandeilo beds, rest discordantly sometimes on the Lower Cambrian beds, at others, on the Laurentian. Lower Silurian Areas. —The principal districts where the Lower Silurian rocks form the surface, are the north and central Highlands and the southern uplands of Scotland, the Lake District of the north of England, the north and centre of Wales, the north-west, north-east, and south-east of Ireland, and the Isle of Man. They also occupy portions of Normandy and Brittany,! where they rest on Cambrian and Laurentian beds, and they have been proved by boring below the Tertiary and Cretaceous strata at Bruxelles (Brussels), Louvain, St. Tron, Menin, and Ostende in Belgium. They also appear at the bottoms of the valleys between the Sambre and the Meuse, as determined by M. Gosselet they probably underlie a large portion of the Paris basin, where they are concealed by Tertiary and Cretaceous formations. Beds of marine origin. —The fossils yielded by the Lower Silurian rocks, whether in the north-west of France, in Belgium, in Wales, in Ireland, or in the north of Scotland,§ all go to prove the marine origin of the strata themselves. They consist chiefly of trilobites, molluscs—cephalopods, gasteropods (lamellibranchs not plentiful), and brachiopods—a few corals, and graptolites. The abundance of these forms in the calcareous beds prove that the waters of the sea teemed with living * Ramsay, supra cit., p. 78. + Murchison “ Siluria,” 4th edit., p. 408. + Quoted by Dr. Mourlon, “ Geol. de la Belgique,” p. 40. § From the Durness, or Assynt, limestone.. 265 Palceo-Geological and Geographiccd Maps of the British Islands. forms. In the Bohemian basin, as M. Barrande* has shown, there was a prodigious development of life ; but often, though many hundreds of feet of slates and grits in some districts, no trace of organic structure is discoverable. Plate XXV. Upper Silurian and Devono-Silurian Periods. The relative areas of land and sea during these periods differ widely from those of the period which preceded it, as will be seen on a comparison of Plates XXIV. and XXV. The sea which overspread the whole of the British Isles and adjoining portions w of France and Belgium is now restricted mainly to the southern and central portions of the British Isles; while large tracts in the north and west, as well as Normandy and Brittany, are converted into land surfaces, holding in their deep depressions, lakes or fresh-water basins, which were formed towards the close of the Silurian period, or in more definite terms, during the Devono-Silurian stage. Nature of the Upper Silurian Beds. —The basement beds of the Upper Silurian series (Llandovery beds) are frequently conglomerates and sandstones, derived from the disintegration of the rocks of the adjoining lands, and by their position we are able to indicate the position of the margins of these lands themselves. Such is the case in the districts of Connemara in the county Galway,f and of Builth in Radnorshire.! The succeeding beds consist of grits, shales and limestones of the Wenlock and Ludlow series, often rich in marine fossils. These beds occur in West Galway and Mayo, in North and South Wales, and Monmouthshire, in Staffordshire, along the southern slopes of the Cumberland mountains, and those of the southern uplands of Scotland. In the north of France and Belgium they are altogether wanting, as the Devonian beds rest against the shelving flanks of ancient lands formed of Lower Silurian and Cambrian strata. § Devono-Silurian Beds. —Under this term I include a series of beds known by various names, and chiefly developed to the north and to the south of the British area. They include the “ Passage beds” of Murchison, and the “ Downton sandstone,” lying at the top of the Upper Ludlow rock, in South Wales ; the “ Dingle and Glengariff Beds ” of Jukes, forming the south-western mountains of Ireland, and seen resting conformably on the Upper Silurian beds along the coast of Dingle : “ the Fintona beds ” of the north of Ireland, which rest unconformably on older crystalline strata ; and the “ Lower Old Red Sandstone ” of Scotland. The Devono- Silurian beds form the connecting series between the Upper Silurian and the estuarine Devonian beds of Monmouth and South Wales, and are probably re- * “Syst. Sil. de la Boheme.” t “ Phys. Geol. of Ireland,” p. 23. | Ramsay, “ Phys. Geol. of England and Wales,” p. 89. § Mourlon, “ Geol. de la Belgique,” t. 1, p. 54. TRANS. ROY. DUB. SOC., N.S., VOL. I. ' 2 Y 266 Palceo-Geological and Geographical Maps of the British Islands. presented south of the Bristol Channel, by the “ Foreland grits and slates ” of North Devon.* These beds were formed by accumulations, sometimes of great thickness, of green, red, and purple sandstones, grits, shales, or slates, and conglomerates—of marine origin, in the southern portion of the British area, but, in the northern, probably of lacustrine origin. In the latter district, according to the views of Professor A. Geikie, the beds of this division of the series were deposited in several distinct lake-basins. One (“ L. Orcadie”), north of the Grampians; a second (“ L. Caledonia”), south of these mountains ; a third (“ L. of Lome”), a district north of Argyleshire, lying at the entrance of the Great Glen ;+ and a fourth (“ L. Cheviot”), on the southern borders of Scotland.^ These deposits were derived from the waste of the adjoining lands formed of the metamorphosed beds of the Highland mountains, but how far they extended in the direction of the Scandinavian promontory is altogether uncertain, so that the eastern limits of these basins must be left undefined. Relations to the adjoining Formations. —Throughout the British area the Upper Silurian beds are unconformable to the Lower Silurian, and in some cases, as in Shropshire, they rest directly on Cambrian beds. In a word, the physical hiatus between the upper and lower divisions of the great Silurian system of Murchison is as marked and complete as it is possible to conceive between any two adjoining sets of strata ; and this being the case, it is not to be wondered at that Sedgwick claimed as “ Cambrian ” all the beds below the Llandovery horizon. After the close of the Lower Silurian epoch, represented by the “ Bala Beds,” there occurred, over the region in question, terrestrial disturbances of great intensity, accompanied in the north of Ireland and Scotland by metamorphic action.§ Large tracts of the ocean bed were converted into land surfaces, while denudation ensued on a great scale, owing to which the uppermost Lower Silurian beds were washed away, and on the resubmergence of the depressed tracts, these materials were used up in the construction of the basement beds of the succeeding Upper Silurian series. Depression then went on, during which the Wenlock and Ludlow beds were formed under tranquil waters, and towards the close of the latter period, the * “ On a proposed Devono-Silurian Formation,” Quart. Journ., Geo. Soc., May, 1882, p. 200; also Trans. Roy. Dub. Soc., vol. i., antea p. 147 (1880). t “ On the Old Red Sandstone of Western Europe.” Part I., Trans. Roy. Soc. Edin., vol. xxviii. The margins of these basins drawn on the maps (Plate XXV., Fig. 2), are very much those indicated by Prof. Geikie. He considers that Lakes “ Orcadie ” and “ Caledonia ” were never united. t It seems probable that in its earlier condition this lake was connected with the sea, but was subsequently disconnected. § That this metamorphism of the Lower Silurian beds of the North British area took place before the Upper Silurian period was first pointed out by Harkness in his paper “ On the Age of the Rocks of West Galway,” &c. Quart. Journ. Geol. Soc., vol. xxii., and has more recently been insisted on by myself in the “ Phys. Geol. and Geog. of Ireland,” p. 22 (1878). 267 Palceo-Geological and Geographical Maps of the British Islands. great lakes of Scotland and of the north of Ireland, bounded on all sides by metamorphosed strata, were formed, while vast masses of material were accumulated over the region of the south-west of Ireland, but in this instance, probably under the ocean. Upper Silurian Areas. The principal areas of this series are to be found along the eastern borders of Wales, extending from the north coast at Conway southwards through Montgomeryshire, Shropshire, Radnor, into Hereford and Monmouth. Isolated portions rise from below the South Staffordshire coalfield, as at Dudley. Eastwards these beds extend under the Cretaceous rocks, and have been proved by borings at Ware* in Hertfordshire, and no doubt, they extend eastwards to the coast. But in Belgium the Upper Silurian rocks are unrepresented, and the Devonian rocks lie in a trough, having the Lower Silurian beds of Brabant on the north, and the Cambrian beds of the Ardennes on the south, against the flanks of which the more recent strata were originally deposited. + As the “ Devono-Silurian ” beds are in all probability represented by the “ SysUme Gedinnien ” (in part at least) at the base of the Devonian Series, they are represented in Plate XXY. Fig. 1, and the sea area is extended over the north of France and Belgium, along the line of this old trough. The Upper Silurian beds lie along the southern flanks of the Cumberland mountains, having a southerly dip, and probably extend eastwards under the Carboniferous rocks to the coast. They again occur along the flanks of the southern uplands of Scotland, where they were probably separated from the sea, and towards the close of that epoch the area was converted into a lake, in which were deposited the beds of the Devono-Silurian series (Lower Old Red Sandstone) near St. Abb’s Head. In Ireland, Upper Silurian Beds occur in Dingle (Kerry), passing upwards into the Devono-Silurian, or Dingle Beds they also occupy considerable tracts on both sides of Killary Harbour and the shores of L. Mask ; and they are again found forming a small tract on the borders of Roscommon and Sligo. The areas of the Devono-Silurian beds have already been stated. Distribution of Land and Sea. —As will be seen by referring to the map (Fig. 2, Plate XXV.), the land areas of the region now under description lay both towards the north and towards the south, between which there was a gulf of moderate d epth extending over the region of the south of Ireland, England, and the north of France, under which the marine strata were deposited. This gulf threw out an arm towards the north, but how far it stretched beyond the eastern coast-line it is impossible to say. The land area of the north was probably a prolongation of the Scandinavian promontory, while large tracts of the Atlantic to the westward formed continuous *Mr. R. Etheridge, f.r.s., The Times, 19th May, 1879. f Dr. Mourlon, Geol. de la Belgique, t. 1, p. 54. t Expl. Mem. Geol. Survey, Sheets 160 and 170. 268 Palceo-Geological and Geographical Maps of the British Islands. land with the northern Highlands of Scotland and Ireland. The western and northern limits of this land area are incapable of definition; it may have included isolated basins besides those we are able to identify in North Britain. At the commencement of the period we are now dealing with, land prevailed to a much greater extent than that shown in the.map, but as time went on, the areas of the sea and inland lakes were extended down to the close of the Devono-Silurian period. Plate XXVI. Ihe Devonian Period. The epoch represented in Figures 1 and 2, Plate XXYI., is that ranging through the Lower and Middle Devonian stages, embracing the beds of the “ Lynton,” “ Hangman,” “ Ilfracombe,” and “ Morthoe ” divisions of Devonshire, and those lying between the Systeme Gedinnien, and the Calcaire de Frasne of Belgium. This series, several thousand feet in thickness, is entirely marine. It is laid open in North and South Devon in England, passes below the Cretaceous rocks of the Thames valley, and re-appears in numerous sections along the river valleys of Belgium, such as those of the Sambre, the Meuse, and the Ourthe, as well as along the valley of the Rhine and its tributaries. In a somewhat altered form it occupies a large tract of country bordering the valleys of the Usk and the Wye, in Monmouthshire and Herefordshire, and is generally, but erroneously as I believe, called by the name of “ Old Red Sandstone.” These last-named beds, I consider to have been deposited in an estuary, bounded towards the north-west and northeast by Silurian lands, but opening southwards into the sea, in which the Devonian beds were being contemporaneously formed. I have, therefore, called these beds “Estuarine Devonian.”* From the remainder of the British Islands, including the whole of Ireland and Scotland, the Lower and Middie Devonian beds are absent, owing to causes which I shall presently endeavour to explain.! Nature of the Devonian Beds. —From what has been said, it will be inferred that the Devonian beds south of the Severn differ in some characters from their representatives north of that river. South of the Severn the formation consists of beds of grit, shales, and limestone, in alternating masses, highly fossiliferous, and yielding remains of molluscs, corals, and crinoids, and some plants. J North of the Severn the beds consist of red and * “ On the Relations of the Rocks of the South of Ireland to those of North Devon, &c.”—Quart. Joum. Geol. Soc., May, 1880, p. 268. The term used in this paper is “lacustrine.” I have since preferred the term estuarine. ! As I have shown in the paper above referred to.— Ibid., pp. 264 and 270-3. Mr. Etheridge in his Presidential address expresses his concurrence in my views.—Quart. Journ. Geol. Soc., May, 1881, p. 193, et seq. + Mr. Etheridge has given a complete account of the fauna of Devonshire in his Presidential address, supra dt. He enumerates no less than 235 species as occurring in the.Middle Devonian beds of South Devon. 269 Palceo-Geological and Geographical Maps of the British Islands. gray marls, with earthy calcareous hands (“cornstones ”), and red or purple sandstones. Fish remains are present in the cornstones, but some examples of Lingida in the lower beds, and of Serpula in the upper, are all the evidences of invertebrate life which, up to the present, they have presented to us. In South Devon the limestones are more massive, but it is not till we examine the sections in the Meuse and Ourthe, in Belgium, that we are able to appreciate the extent to which marine limestones were developed at this period. Relations with the adjoining Formations. —Confining our attention to the region of the south of England, the Devonian strata may be considered as forming a complete connecting series with the Upper Silurian and Devono-Silurian beds below and the Carboniferous beds above. Over this region, deposition of sediment appears to have proceeded with but few interruptions, of which none are marked by visible physical breaks. After the close of the Silurian period, depression went on, and various kinds of sediment were formed over the floor of the sea-bed, during slow subsidence over this area. Meanwhile the fauna of the previous period, modified as regards species, but largely similar as regards genera, re-appeared under new forms; and as Mr. Lonsdale long ago observed, presents generally a facies, intermediate between that of the Carboniferous, on the one hand, and of the Silurian, on the other. Mr. Etheridge recognises about 550 species as belonging to the British Devonian group. Absence of Devonian Beds in the North and West of the British Isles. —The absence of representatives of the marine Devonian beds of the south of England over the Irish and Scottish areas is a circumstance which, in my opinion, can only be satisfactorily accounted for in one way, namely, that these areas had been elevated into dry land during the time that the south of England and adjoining continental regions were submerged beneath the waters of the Devonian sea, and became the receptacles of Devonian sediment.* As confirming this view we have the fact that the Upper Devonian, or Old Red Sandstone proper, is everywhere unconformable to the beds on which it rests in Ireland and Scotland, whether these belong to the Devono-Silurian or still older formations.! There is, therefore, in these countries a gap, or hiatus, of a very decided character, which is not the case in Devonshire, where the whole series, from the top of the Silurian to the base of the Carboniferous series, is complete. This northern and western hiatus is, in fact, filled up in Devonshire owing to the presence of the Lower and Middle Devonian beds, which are absent in Ireland and Scotland. * This view was first proposed in the Geological Magazine, and was afterwards more fully unfolded in the paper above cited, and in the Trans. Roy. Dublin Soo., vol. i., antea p. 147, &c. t This is distinctly enforced by Sir R. Griffith as regards Ireland, and is exemplified in many sections, especially those of the Dingle promontory; and by Professor Geikie as regards Scotland. There may, also, be a slight unconformity at the base of the yellow sandstone in S. Wales, in keeping with that of the adjoining Irish area. 270 Palceo-Geological and Geographical Maps of the British Islands. The unconformity between the Upper Devonian Sandstone (or Upper Old Red Sandstone), and the Devono-Silurian beds (i.e. the “ Dingle beds ” of Ireland, and the “ Lower Old Red Sandstone ” of Scotland), indicates that after their deposition these beds were subjected to disturbances, were elevated into land surfaces, and exposed to denudation. In this position they remained throughout the Lower and Middle Devonian periods, and were only resubmerged when that of the Upper Devonian set in. Plate XXVI., Fig. 2, represents the period of elevation of the west and north of the British Isles, and of the concurrent depression of the region to the south. It is probable, also, that the centre and north of France (Normandy, Britany, and the Ardennes), were in a condition of land-surfaces during the deposition of the Lower and Middle Devonian beds, as these everywhere rest, and with varying geological horizons, against the older formations of which this part of France is largely formed. We must also recollect that the whole area of the south of the British Isles, and of the adjoining parts of the continent, has undergone enormous lateral compression, in a north and south direction, owing to which the originally horizontal Devonian and Carboniferous beds have been crushed into numerous sharp foldings and flexures, lying along approximately east and west axes, and that these extend from the extremity of Kerry and Cork through Devonshire, under the Thames valley, and reappear in Fi'ance and Belgium, and as far as the banks of the Rhine. If, therefore, we wish to realize the geographical position of the Devonian beds as originally deposited, we must reduce these flexures of the beds to the horizontal position, in which case the present apparently narrow trough running across the south of England and north of France would be spread out to probably almost twice its present width.* Distribution of Land and Sea. —On the above grounds, therefore, I have represented in Figure 2, the whole of the western and northern portions of the British Islands, with the adjoining portions now covered by the ocean, as land during the Middle Devonian period. Contemporaneously with this the sea extended over the south of England, and eastwards into Germany, under the waters of which were deposited in England the fossiliferous limestones of Ilfracombe and Plymouth ; in Belgium, the “ Calcaire de Givetand in Germany, the “ Stringocephalus limestone.” Once we thoroughly understand the physical relations of these different areas, the reasons for the present distribution of strata become clear. * The flexuring of these beds, as laid open along the Meuse, is very well shown by M. Gosselet in a drawing, as copied by Dr. Mourlon, in the “ Geol. de la Belgique,” t. 1, p. 56. As the average angle of inclination exceeds 45°, the original length would have been in this case more than twice the present. Palao-Geological and Geographical Maps of the British Islands. 271 Plate XXVII. Old Red Sandstone and Lower Carboniferous Periods. In order to save the engraving of a separate plate, I have endeavoured to include the above sets of strata in one pair of maps, although the Old Red Sandstone is a member of the Upper Devonian Series, rather than of the Carboniferous. This is proved by the occurrence of Old Red fishes ( Coccosteus , Pterichthys, Asterolepis, &c.), together with plants ( Adiantites Hibernicus), and fresh-water molluscs ( Anodonta Jukcsii), in the beds of this formation in Ireland. In many districts, however, the Old Red Sandstone appears to be conformable to the overly ing Low er Carboniferous beds, while unconfonnable to all strata older than the Middle Devonian beds, and as these are only present in the south of England, Belgium, and France, the Old Red Sandstone is elsewhere unconfonnable to the strata on which it reposes. The strata included in Plate XXVII., range from the Old Red Sandstone or Conglomerate to the top of the Carboniferous Limestone. At the commencement of the deposition of these beds the greater part of the area now described existed as land. But as time went on, the British area became depressed, and the sea gradually gained on the land; so that, at its close, only the northern and western tracts were unsubmerged, together with portions of the border districts of Scotland. The Cumberland mountains, and a tract ranging* from North Wales, Shropshire, and the centre to the east of England was also unsubmerged. Over the submerged areas the Lower Carboniferous strata were deposited; from the unsubmerged districts they are absent. Throughout South Staffordshire, parts of Salop, Leicestershire, and Warwickshire, the Upper and Middle Carboniferous beds rest directly on the Silurian or Cambrian beds.f Nature of the Old Red Sandstone. —The Old Red Sandstone is found over the S. of Ireland in the form of a massive conglomerate, forming fine escarpments in the Commeragh and Dingle mountains, and passing upwards into finer red sandstones, and beds of flagstone and shale. The uppermost beds, called the “ Kiltorcan beds,” contain fish-remains, a fresh-water mussel ( Anadonta Jukesii), and plants. They are lucustrine deposits over the area of the south of Ireland, and mark the upper limit of the Old Red Sandstone. In South Wales, along the northern margin of the coal-basin, the Old Red Sandstone forms bold cliffs, rising from below the Carboniferous limestone and shale, and consists of yellow sandstone and conglomerate. In North Devon, it is * It is possible that the sea may have spread between North Wales and the Wicklow mountains during this time. j South of Halesowen, the Upper Silurian beds were penetrated by a coal-shaft under the Upper Coal-measurer., and at Dudley, Forest of Wyre, Shrewsbury, &c., the Upper Coal-measures rest on Lower Palaeozoic beds. 272 Palceo-Geological and Geographical Maps of the British Islands. represented by the “ Pickwell Down sandstone,”* occupying a similar position below the “ Pilton and Marwood beds.” In Belgium and France, it is represented by the “ Psammite du Condroz,” of the Upper Devonian Series, and in Scotland, by Red Sandstone and Conglomerate, unconformable to the “ Lower Old Red ” (or Devono-Silurian) beds. It is scarcely represented in the north of England.! Lower Carboniferous Beds. —These immediately succeed the “ Kiltorcan beds,” in the south of Ireland, and there consist of gray grits and slates (“ Coom- hola grits ”) passing upwards into the “ Carboniferous slate ” and limestone. In the north of Ireland, the “ Coomhola beds,” &c., are represented by massive yellowish grits and shales, with a conglomerate base. The Carboniferous limestone forms the greater portion of the central plain of Ireland. In Scotland the base of the Carboniferous series is called the “ Calciferous sandstone,” and the limestone is represented by that of the Roman camp near Edinburgh. In the north of England, the “ Scar limestone ” forms step-like escarpments, and in Derbyshire rises into hills of 2,000 feet, dipping down towards the east and west below the Yoredale beds and millstone grit. In South Wales the limestone forms a range of fine escarpments along the north of the great coal-basin, resting on the shales, and passing below the millstone grit. In North Devon these shales are represented by the “ Marwood,” “ Pilton,” and “Barnstaple” beds, as already stated. The Carboniferous limestone, however, is a debased formation as compared with its representative further north. In Belgium the Carboniferous limestone is nobly developed and immediately underlies the coal formation.^ The following Table of Synonyms may prove useful :— Middle Carboniferous, . Lower Carboniferous, . Old Red Sandstone (Upper). " England. Gannister Beds, Millstone Grit, Yoredale Beds, Mountain Lime- Carboniferous stone. Limestone. Table of Synonyms. Ireland. Scotland. Belgium.t Lower Coal-Mea- Slaty Black-band Schistes de Chokier. sures. Series. . Millstone Grit, or Moorstone Rock. Flags. Upper Limestone, and Lower Coal and Ironstone Series. Roman Camp Limestone. Shale Series, f Absent, in some places as Liege, but present in others. ■ Calcaire de Dinant. Limestone Shale,^or \CarboniferousSlate, j UPP^.^ (^Schistes de la Fa- BedtP^ Jr ' lit011 j" Coomhola Grit, &c. Yellow Sandstone' Calciferous Sandstone. j menne. and Conglomerate. Pickwell Down Kiltorcan Beds,' Old Red Sand-(Upper Old Red 1 Psammite du Con- stone and Con- (’ Sandstone. j" droz (lower part.) glomerate. Sandstone (Devonshire.) * Scient. Trans., Roy. Dub. Soc., vol. i., antea p. 147.—Etheridge, Quart. Journ. Geol. Soc., vol. xxxvii., p. 196. | For a full account of the representative series given above, see Quart. Journ., Geol. Soc., vol. xxxii. pp. 613-651. + In Belgium the lower coal-measures sometimes, but not always, rest unconformably on the limestone, the millstone grit and Yoredale beds being then absent. This was explained to me by Dr. De Koninck, at Liege. 273 Palceo-Geological and Geographical Maps of the British Islands. Distribution of Land and Sea. —At the commencement of the Upper Devonian stage nearly the whole of the centre and north of Ireland, the north of Scotland, the centre and north of England and Wales, were dry land, but in the southern portions of the British Isles and adjoining parts of the Continent there was an area of depression. Over the south of Ireland there appears to have been formed a fresh-water lake, in which the Old Red Sandstone was deposited in the form of shino-le and finer sediment drained from off the adjoining lands formed of Silurian and Devono-Silurian beds which had been previously elevated into land over the region of Kerry, Cork, and Waterford. The waters of this lake were inhabited by numerous fishes and the large mussel, Anodonta Jukesii, while the adjoining lands were covered by a luxuriant vegetation, the representatives of which are preserved to us in “ The Kiltorcan beds.” This lake may have extended eastwards into the south of England, but in France and Belgium it gave place to marine conditions, as the representative strata known as the “ Psammite du Coudroz ” are of marine origin.* In Scotland the yellow sandstone and conglomerate, with Holoptychius and Cyclopteris (Palseopteris) Hibernica, was probably deposited within lacustrine waters. On the commencement of the Lower Carboniferous stage the sea everywhere occupied the submerged tracts, bathing the sides of the uplands and mountainous parts, and bringing with it multitudes of marine animals, so that the oldest Carboniferous strata in Ireland, England and Wales, and Scotland contain numerous marine forms.! During the subsequent epoch of the Carboniferous Limestone the depression proceeded, and the sea ascended on the flanks of the uplands until only the very highest elevations were left uncovered. Deep sea conditions prevailed over the north and south of England and the centre of Ireland, and here the calcareous beds were formed in greatest thickness and purity through organic agency. A tract of country extending across England, from Shropshire through Worcestershire and South Staffordshire, into the eastern counties appears to have remained as a ridge or land barrier, separating the basin of the north of England from that of the south, as the Lower Carboniferous rocks are absent, or only present as thin marginal representatives along this line of country.* In Plate XXVII., figure 2, the relations of sea and land are indicated, as far as possible, during the middle of the epoch of the Carboniferous Limestone. It is also probable that the old rocks of the north-west of France were unsubmerged, as the little detached coalfields of the centre of that country rest directly on these rocks * Here it contains marine fossils, suck as Spirifer disjunctus, Rhynchonella pleurodon, with plants Lepidodendron notum, Sphenopteris flaccida, and a variety of Palmopteris Hibernica. Mourlon. Loc. cit., p. 88. t See preceding Table of Synonyms, page 272. | The existence of such a ridge was hrst indicated by the late Professor Jukes, and subsequently described in “ The Coal Fields of Great Britain.” The discovery of Carboniferous Limestone at a depth, of 890 feet below Northampton shows that the ridge was south of this spot. Etheridge; Quart. Journ. Geol. Soc., vol. xxxvii., p. 231. TUANS, nor. DCB. SOC.,N.S. VOL. I. 2Z 274 Paloeo-Geological and Geographical Maps of the British Islands. without the intervention of the Lower Carboniferous beds ; at the same time, over the region lying along the borders of France and Belgium, the waters of the Lower Carboniferous sea prevailed, and the limestone formation is grandly represented. Plate XXVIII. Upper Carboniferous Period. The Upper Carboniferous strata are the chief depositories of coal in the British Isles and the adjoining continental districts. They are separated from the Lower Carboniferous strata represented in Plate XXVII., by the middle division of the system, including the following in descending order :—* Middle ( 1. The Gannister Beds, or Lower Coal-measures. Carboniferous J 2. The Millstone Grit, or Flagstone Series of Ireland. Series. ^ 3. Tire Yoredale Beds, or Upper Shale Series of Ireland. All the above are essentially of marine origin ; those of theTJpper Carboniferous series are of estuarine or lacustrine origin, with occasional marine bands at distant intervals. Nature of the Upper Carboniferous Beds. —The strata included under this head consist of two divisions; the Lower, or Middle Coal-measures, consisting of yellow and gray sandstones, blue and black clays and shales, bands of coal and ironstone. They contain plants, bivalves (Anthracosia) , and fish remains. The occasional marine bands are to be recognised by the fossils. The Upper Coal-measures consist of reddish and purple sandstones, red and gray clays and shales, thin bands of coal, ironstone and limestone, with Spirorbis carbonarius, and fish. These two divisions combined attain, in Lancashire, a thickness of 5,000 to 6,000 feet, but thin away rapidly in the direction of Leicestershire and Warwickshire. In Belgium these beds are also of great thickness, though the uppermost have generally been denuded away. Distribution of Strata. —The Coal-measures of England and Scotland were originally distributed in two, or possibly three, large sheets, lying to the north and south of a central ridge, ranging from North Wales through Shropshire eastwards.! This I have called the central barrier (Fig. 2). It is uncertain whether it was not connected with the ridge of the Wicklow Mountains across the Irish Channel. This old ridge may be a prolongation of a land area stretching southwards from Scandinavia, and it existed in wider dimensions during the Lower Carboniferous period.! It is also uncertain whether the coal-measures of Scotland stretched * This is a classification proposed in my paper “ On the Upper Limits of the essentially marine beds of the Carboniferous group, &c.” Quart. Journ., Geol. Soc., Vol. XXXII., pp. 013-651. It has not been considered necessary to prepare a plate of this division, which would be intermediate in its arrangements between Plates XXYII. and XXVIII. f The evidences of this ridge cannot here be discussed, but the reader is referred to the Geological Survey Memoir, “ On the Triassic and Permian Bocks of the Central Counties of England; ” also to the “ Coalfields of Great Britain.” 4th edition, p. 520. + Compare Fig. 2, in Plate XXVIII., with that in Plate XXVII. 275 Palm-Geological and Geographical Maps of the British Islands. continuously across the south of Scotland to join those of the north of England. It has been assumed that some of the higher parts of the southern uplands were uncovered by Upper Carboniferous strata, as they certainly were by those of the preceding stage. Nearly the whole of Ireland was originally covered by coal- measures.* Formation of Coalfields. — Out of the original extensive tracts of coal-measures, almost conterminous with the boundaries of submerged areas shown in figure 2, the existing coalfields have been constructed. As compared with the original areas, their size is small indeed. This is due to the extensive denudations which took place—first, at the close of the Carboniferous period ; second, at the close of the Permian period ; and thirdly, in still more recent times. Ireland has suffered most of all, owing to the absence of mesozoic strata ;f only small isolated patches, monuments of former more extended tracts, have been left behind. The possible positions of three coal-basins south of the Thames valley are shown in figure 2, very much the positions originally indicated by Mr. R. Good win-Austen. J The sub-Wealden boring, intended to ascertain the nature of the Palaeozoic strata along this tract, unfortunately was stopped before passing into Palaeozoic rocks. The position of the coal-measures—proved under the Lias by boring at Burford—is also shown in Figure 1, but it is impossible to determine the form of this coal-basin. Distribution of Land and Water. —Little need be added to what has already been said on this point. As compared with the Lower. Carboniferous epoch, the land areas become contracted owing to subsidence, but the thickening of the strata, both towards the north-west and south-west of England, indicate the existence of extensive tracts of land, and sources of sediment, in those directions.? The waters which overspread the plains were disconnected from those of the ocean, except at intervals, though possibly at all times bordering on the sea-level of the period. Plate XXIX. The Permian Period. The Permian beds are restricted to the central portions of the British Isles, and apparently were never deposited over any part of the extreme northern, western, or southern districts, or of the adjoining continental areas. According to the view of Sir A. Ramsay, the magnesian limestone of the north of England was formed * See “Physical Geology and Geography of Ireland,” pp. 43, 149, 163. t Ibid., p. 164. X Quart. Journ. Geol. Soc., vol. xi. (1855.) The same author places the line of possible coal-measure under the Thames valley, but the London borings for water do not appear to me to bear out this view. See Map, No. 6, to accompanying evidence before the Royal Coal Commission. The extension of the Coal-measures beneath newer formations is indicated by the lighter shade in figure 1. §See, on this subject, my paper “ On Iso-diametric Lines, &c.” Quart. Joum. Geol. Soc., vol. xviii. pp. 127-146 (1862). 27G Palm-Geological and Geographical Maps of the British Islands. under the waters of an inland sea, like the Baltic or Caspian, the fauna being exceedingly sparce, as compared with that of the limestones of the Carboniferous period,* and indicative of the absence of open oceanic waters. The region of the magnesian limestone of the north of England appears to have been disconnected with that of the central counties and Shropshire by a barrier ridge, the position of which is indicated in Figure 2. To the south and west of this ridge, only Lower Permian beds are found,! and it is probable that these latter beds are, in the main, lacustrine. The Permian beds of Scotland are restricted to the south of that country, and those of Ireland to the districts of Down, Tyrone, and Armagh. Nature of the Permian Beds. —Owing to the dissimilarity of the Permian beds lying on either side of the Carboniferous ridge above referred to, I have arranged the Permian strata under two heads or types—those of the “Lancastrian” and “ Salopian.’’^ The beds of the “ Lancastrian type ” belong to the north of England, and may thus be described in the west and east of that area :— Permian Beds of the Lancastrian type§ West. East. I Bands of limestone, sometimes magnesian, / Marls. \ Upper Division. < with red marls. Fossils— Turbo, liissoa, ) Upper Limestone. (Fossils, ( JVatica, Axinus, Schizodus, The majority of the above specimens had evidently been transported from the district of Cumberland and North Lancashire, which we may suppose sent off loads of stones and boulders southwards upon ice-bergs and rafts. The upper boulder clay rises to elevations of 500-600 feet amongst the western slopes of the Lancashire hills, and marine shells (Turritella terebra, Fusus Bamjius, Purpura lapilltis, &c.) have been found in it; as, for instance, at Hollingworth Reservoir (568 feet above the sea), the vale of Mottram, Bradbury and Hyde.J From this elevation it gently slopes southward and westward, towards the plain of Cheshire,§ which is largely overspread by it; it occupies portion's of the low valleys of North Wales.ll On the other hand, the Pennine table-land of South Yorkshire and North Derbyshire, and the low country to the east of it are free from drift deposits,^ a state of things very difficult to explain, but clearly indicating the absence of glacial conditions amongst the eastern valleys of the Pennine chain south of the parallel of 53° 35' N. lat. * This is described by Mr. S. J. Wood as a deposit of clay containing a few scattered stones and boulders when the sea extended over the land to an extent not exceeding 350 or 400 feet anywhere in Yorkshire. Geol. Magazine, vol. vii. 4 jjy Professor Ramsay and the author. “ Geol. of Oldham, &c., Mem. Geol. Survey (1864). + By Mr. Bateman, c.e., Professor Prestirch, and Mr. John Taylor. “GeoL of Oldham, &c.,” Mem. Geol. Survey (1864), p. 51. § “Geol. of North Derbyshire.” Ibid, p. 75. || In a pit by the railway side, near Abergele, it may be observed capping the interglacial gravels at an elevation of only 20-30 feet above high water. H “ Geol. of Dewsbury, &c.,” Mem. Geol. Survey, p. 20 (1871). 294 Palceo-Geological and Geographical Maps of the British Islands. In Ireland the upper boulder clay, resting on the marine gravels of the interglacial stage, has been noticed in several places, as at Killiney near Dublin, along the Wexford coast,* at the marble quarries near Kilkenny,! at Modabeagh colliery near Carlow,J and in Counties Tyrone, Antrim, and Derry. It is similar to its English representative, but has probably suffered more from denudation, so that it is only to be found in small detached areas. When it was in course of formation the land was in places probably depressed to a level of about 1,000 feet below that it now occupies, and as the sea-bed still further rose, the soft material of which it was composed would have offered but slight resistance to the waves and currents which chafed around the unprotected prominences. In more than one instance which has come under my notice, the formation would seem only to be represented by blocks of travelled stone stranded on the surface. An instance of this kind occurs at Kilkelly, in Co. Mayo, where large slabs of Carboniferous grit are to be found strewn over a tract of country of considerable extent, covered by a thick deposit of gravel on which these blocks are found resting.? When we turn to Scotland we are met by difficulties of identification, as the geologists of that country do not seem to have recognised a representative to the Upper Boulder Clay.|| Dr. J. Geikie refers to the “ Upper Drift Deposits,” very diverse materials, such as coarse, earthy debris of angular fragments, and large blocks and boulders wdiich are strewn over the northern slopes of the southern uplands. These he traces to the Grampians as their source, and considers they have been brought to their present position on a second great sheet of ice moving southward.^ It is, of course possible that the more northerly positions, the greater elevation of the Grampians and North Highland mountains than those of other British districts, and the consequently greater amount of snow and ice which must have accumulated on their summits and slopes, may have produced a second ice sheet which has no representative elsewhere ; and in such a case, the central valley, though really below the sea level, and submerged to a depth perhaps of several hundreds of feet, may have been completely filled with ice, which for a time excluded the waters of the sea. But admitting all this, it is inevitable that when the ice began to give way, owing to the approaching amelioration of the climate, it would be * Professor Harkuess, “ Geol. Magazine,” vol. vi., p. 542. t “ Phys. Geol. Ireland,” p. 90. Geikie, “ Great Ice Age,” 2nd edit. f Hardman, Journ. Roy. Geol. Soc., vol. iv., p. 73 ; Expl. Mem., Sheet 35 of the Maps Geol. Survey. Here the Upper Boulder Olay was jjroved to he 84 feet in thickness, resting on 25 feet of sands, gravels, and clays, and this again on Lower Boulder Clay 8 feet. The elevation is about 750 feet. § Originally described by Sir R. Griffith, Brit. Assoc. Rep. 1844. || My own observations in the Glasgow district, however (1868-9), lead me to think that such a deposit may occur east of that city. 'I Loc. cit. 295 Palceo-Geological and Geographical Maps of the British Islands. broken up into rafts and bergs answering in all respects the description given of the phenomena in England and Ireland.* The local moraines which existed amongst the higher unsubmerged districts, became centres of dispersion of erratics which were floated to their destination on masses of glacier ice. If (as Dr. Geikie considers) about the time now referred to, the south of Scotland was submerged to the depth of 1,100, or even 1,250 feet,t and the north of England and of Ireland to a depth of about 900 or 1,000 feet, the tract submerged would be very large, and boulders would be carried in directions corresponding to the prevalent winds and currents. The courses travelled by such erratics have been ably traced by, amongst others, Mr. D. Mackintosh, who has traced the boulders over large tracts of country in the north-west and centre of England and Wales to their parent masses.+ Amongst the more remarkable instances of erratic blocks are those at Pagham and Selsea, mentioned by Lyell.§ It is unnecessary for my present purpose to go more fully into the details of later glacial and post-glacial phenomena. It will probably suffice that I should add that the climaticand geographical conditions of the stage of the Upper Boulder Clay gradually gave place to those which preceded, and ultimately introduced the existing temperate condition of climate. The land gradually rose out of the sea, the rise being probably accompanied by prolonged pauses. The snows and glaciers melted off the mountains. The sea was gradually freed from ice, and the waters became pure and limpid. The plants and animals of the adjoining continent once again flocked over and restored life and verdure to the face of nature. Man, himself, followed in their train, and made his dwelling in the caves of the rocks, living by the chase, and trying his strength with some of the fierce carnivores which infested the forests and dens of the mountains. || With this state of affairs geology closes its record, and makes way for the researches of the antiquarian and historian. It will be observed that in the maps referring to the glacial period (Plates XXXIV. and XXXV.) I have represented only the supposed physical restorations of the surface of the country as they were during the three special stages to which they point. I have not attempted to produce corresponding maps showing the distribution of the various glacial deposits. To attempt this would have been impossible on a scale so small as those of these three little maps, even if I had had the necessary materials to guide me. But such is not the case. The mapping of * Dr. Geikie, and also Mr. Jamieson (Quart. Journ. Geol. Soc., 1865) have treated very fully of the formation of kames (in Ireland called “ eskers ”), which the former refers to the upper glacial deposits, hut I prefer (for reasons I have stated elsewhere, “ Phys. Geol. of Ireland,” p. 100) to regard them as post-glacial. The phenomena in Ireland are very similar to those of Scotland. t From Mr. H. M. Skae’s observations in Nithsdale. + Quart. Journ. Geol. Soc., London, 1879-82. § “ Antiquity of Man.” p. 280. || I place the advent of man as post-glacial deliberately, as Mr. John Evans, f.r.s., our highest authority on such questions, has recently analysed the evidences which have been adduced both in Europe and the British Isles, for assigning to him a pre-glacial advent, and finds them in all cases more or less untrustworthy. 296 Palceo-Geological and Geographical Maps of the British Islands. the Quaternary deposits in detail has as yet been very partially carried out by the Government surveyors, or by private agency, and it is of such a character that it could not be effectively reproduced on a single map unless one of a scale not smaller than 10 miles to the inch, or °f nature.* * * § The Upper Boulder Clay referred to above, indicates the recurrence of glacial conditions, but not to the extent of those which prevailed during the formation of the Lower Boulder Clay or Till. In Lancashire and Cheshire this deposit may be seen resting on the interglacial gravels and sands in the banks of the Bibble above Preston, and on the coast near Southport, as well as in many other places. It consists of red clay with stones and small boulders often glaciated, but the clay is laminated, and was evidently formed under water. In the east of England, however, it seems to be represented by a second formation of boulder clay formed by a second protrusion of Scandinavian ice, and known as “ the great chalky boulder clay,” described by Messrs. Wood and Rome as a “ lead-coloured clay abounding in chalk debris accompanied by stones and boulders of all sorts of rocks.”t It has been traced from Holderness and the Yale of York and identified with a similar deposit in Norfolk and Suffolk. In Ireland the Upper Boulder Clay has been recognised in numerous places, as at Kilkennyand other central and northern localities. § * The minute divisions of the Quaternary series are being carefully laid down on the Government maps of Belgium, “ Commission de la Carte Geologique,” under the department of the Minister of the Interior, but the scale is a large one, viz. : t Quart. Journ. Geol. Soc., vol. xxiv. Mr. S. V. Wood has contributed still more recently another elaborate account of the glacial beds of this part of England. + See woodcut and section ; Geikie, “ Great Ice Age,” 2nd edit., p. 395-6. § Hardman, Journ. Roy. Geol. Soc., Ireland, vol. iv., new ser., p. 73. Trans. R.D.S. n.s. Vol. r. Physical Maps of the Laurentian Period. Hate XXII EXPLANATION / \ / sed Areas LOCALITIES. I Norway S. Sweden foNWlnah land. /o OaterHeb7'ides 4 DcneadV 5 'fyi'cne? £ Sitae Sc I BeJmullet 8 Galway Ajujlf ' sea . ; llyonnauca II ftnJJany IZ yend . ee . 13 Cenltxtl /vaster ? HBofteaase &c Forster $■ C d UiJl DubUa, Trans. R.D.S. n.s. Vol. I. PHYSICAL MAPS OF THE CAMBRIAN PERIOD. Plate XXIII. s a . forsl&' A C tyilfv, Dtibluv Trans. R.D.S. n.s. Vol. 1. PHYSICAL MAPS OF THE LOWER SlLURIAN PERIOD. Plate XXIV.. Q n V ' o : Q '■ ^ «•-* c-s ^ ts cri S S \\ Trans. R.D.S. n.s. Vol. I. PHYSICAL MAPS OF THE UPPER SILURIAN AND DEVONO-Si LU RI AN PERIODS. Plate XXV. Q K ^ 'Q Cp v~ 7 ©1§L\ S §‘S 3 „ 't 3 - Uliiinissfii ““ sjrsi jT, j <7 A "7 V. TbrstfT S C p Lille, DuMaiv. Physical Maps of the Lower and Middle Devonian Periods. piat« xxvi Tcrsler $ C c LiXhJDablAJb Physical Maps of the Old Red Sandstone and Lower Carboniferous Periods. tui lerster HC? fjilh,Dul>Un, Trans. R.D.S. n.s. Vol. I. PHYSICAL MAPS OF THE PERMIAN PERIOD. Plate XXIX. ^ C-> ^ cvsler & C?Jjith. r T}aJ)tiJL. JvrsttT $,C c JAXh.,Duj.%uv % .■ 11 x ,§| I ^ Q K ^ JFcrster & C v LxXh JJvMhrL Trans. R.D.S. n.s. Vo!. I. PHYSICAL MAPS OF THE CRETACEOUS PERIOD. Plate XXXII. 3\S 7 'tv.'vi Jvrster & C c -LCth.J)abbuh. Middle Tertiary Periods. Phvs/cal Maps of the Lower & M/ddle Tertiary Periods. ,s. a f o JO NlO utlpiQ YfMj ji Trans. R.D.S. n.s. Vol. I. PHYSICAL MAP OF THE LOWER GLACIAL EPOCH. Plate XXXIV. EXHANATIOS Grmi tee Sheet, of _ Xcrwax & Brita/r, hand Surface _ ciltu ut tee, , Ocean Surf her. DUlrtt hnc.s chew the path, ot' the Ice WhitepcfUens Snow fields Aitcws shew direction, of fer flrne M E R Cr L A C E ^ 4 / r Forster & C c l. ith. 1) ublui npiFT PFRIOD iContinued) Plate^XSN Post Pliocene or Drift Period ^continued piatesxxv B Fcrsur&c v j)ntiin. '/xn. /. Map of British. Isles. (furuiif epoch, of lig.Z. J\lap cl BritAsh Isles* durutg epoch _ oj Greatest siihinjCAtjcJice. ilnlljal/ieiaJ) suIj pLaciat ccnaBwtis ( (jpper (jIaamau ’V*.