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GLACIAL PERIOD
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GLACIAL See also:PERIOD , in See also:geology, the name usually given, by See also:English and See also:American writers, to that comparatively See also:recent See also:time when all parts of the See also:world suffered a marked lowering of temperature, accompanied in See also:northern See also:Europe and See also:North See also:America by glacial conditions, not unlike those which now characterize the Polar regions. This period, which is also known as the " See also:Great See also:Ice See also:Age " (See also:German See also:Die Eiszeit), is synchronous with the See also:Pleistocene period, the earlier of the See also:Post-See also:Tertiary or See also:Quaternary divisions of See also:geological time. Although " Glacial period " and " Pleistocene " (q.v.) are often used synonymously it is convenient to consider them separately, inasmuch as not a few Pleistocene formations have no causal relationship with conditions of glaciation. Not until the beginning of the 19th See also:century did the deposits now generally recognized as the result of ice See also:action receive serious See also:attention; the tendency was to regard such superficial and irregular material as See also:mere rubbish. See also:Early ideas upon the subject usually assigned floods as the formative agency, and this view is still not without its supporters (see See also:Sir H. H. Howorth, The Glacial Nightmare and the See also:Flood). Doubtless this attitude was in See also:part due to the See also:comparative rarity of glaciers and ice-See also:fields where the See also:work of ice could be directly observed. It was natural therefore that the first scientific references to glacial action should have been stimulated by the Alpine regions of See also:Switzerland, which called forth the writings of J. J. See also:Scheuchzer, B. F. See also:Kuhn, H. B. de See also:Saussure, F. G. Hugi, and particularly those of J. Venetz, J. G. von See also:Charpentier and L. Aggasiz. See also:Canon Rendu, J. See also:Forbes and others had studied the cause of See also:motion of glaciers, while keen observers, notably Sir See also: However, before this view had become established Sir C. See also:Lyell evolved the " See also:drift theory " to explain the widely spread phenomenon of transported blocks, See also:boulder See also:clay and the allied deposits; in this he was supported by Sir H. de la Beche, See also: See also:Geinitz, A. Helland, Jentzsch, K. Keilhack, A. Penck, H. See also:Schroder, F. Wahnschaffe in Scandinavia and See also:Germany; T. C. Chamberlin, W. Upham, G. F. See also:Wright in North America, have all tended to confirm the view that it is to the See also:movement of glaciers and ice-sheets that we must look as the predominant See also:agent of transport and See also:abrasion in this period. The three stages through which our knowledge of glacial work has advanced may thus be summarized: (I) the diluvial See also:hypothesis, deposits formed by floods; (2) the drift hypothesis, deposits formed mainly by icebergs and floating ice; (3) the ice-See also:sheet hypothesis, deposits formed directly or indirectly through the agency of flowing ice. Evidences.—The evidence relied upon by geologists for the former existence of the great ice-sheets which traversed the northern regions of Europe and America is mainly of two kinds: (I) the See also:peculiar erosion of the older rocks by ice and ice-See also:borne stones, and (2) the nature and disposition of ice-borne rock debris. After having established the criteria by which the work of moving ice is to be recognized in regions of active glaciation, the task of identifying the results of earlier glaciation elsewhere has been carried on with unabated See also:energy.
r. Ice Erosion.—Although there are certain points of difference between the work of glaciers and broad ice-sheets, the former
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Arrows indicate the direction of Ice-See also:flour gym_
being more or less restricted laterally by the valleys in which they flow, the See also:general results of their passage over the rocky See also:floor are essentially similar. Smooth rounded outlines are imparted to the rocks, markedly contrasting with the pinnacled and irregular surfaces produced by See also:ordinary weathering; where these rounded" surfaces have been formed on a See also:minor See also:scale the well-known features of roches moutonnees (German Rundhocker) are created; on a larger scale we have the erosion-See also:form known as " See also:crag and tail," when the ice-sheet has overridden ground with more pronounced contours, the See also:side of the See also: Geikie, See also:Tyndall, Reiland, H. See also:Hess, A. Penck, and others have expressed themselves in favour of a glacial origin; while A. See also:Heim, F. Stapff, T. See also:Kjerulf, L. Rutimeyer and many others have strongly opposed this view. 2. Glacial deposits may be roughly classified in two See also:groups: those that have been formed directly by the action of the ice, and those formed through the agency of water flowing under, upon, and from the ice-sheets, or in streams and lakes modified by the presence of the ice. To differentiate in practice between the results of these two agencies is a See also:matter of some difficulty in the case of unstratified deposits; but the boulder clay may be taken as the typical formation of the See also:glacier or ice-sheet, whether it has been See also:left as a terminal See also:moraine at the limit of glaciation or as a ground moraine beneath the ice. A stratified form of boulder clay, which not infrequently rests upon, and is therefore younger than, the more typical variety, is usually regarded as a See also:deposit formed by water from the material (englacial, innenmoran) held in suspension within the ice, and set See also:free during the See also:process of melting. Besides the innumerable boulders, large and small, embedded in the boulder clay, isolated masses of rock, often of enormous See also:size, have been borne by ice-sheets far from their See also:original See also:home and stranded when the ice melted. These " erratic blocks," " perched blocks " (German Findlinge) are See also:familiar See also:objects in the Alpine glacier districts, where they have frequently received individual names, but they are just as easily recognized in regions from which the glaciers that brought them there have See also:long since been banished. Not only did the ice transport blocks of hard rock, See also:granite and the like, but huge masses of stratified rock were torn from their See also:bed by the same agency; the masses of See also:chalk in the cliffs near See also:Cromer are well known; near See also:Berlin, at Firkenwald, there is a transported See also:mass of chalk estimated to be at least 2,000,000 cubic metres in bulk, which has travelled probably 15 kilometres from its original site; a See also:block of See also:Lincolnshire oolite is recorded by C. See also:Fox-Strangways near Melton in See also:Leicestershire, which is 300 yds. long and roo yds. broad if no more; and instances of a similar See also:kind might be multiplied. When we turn to the " fluvio-glacial " deposits we find a bewildering variety of stratified and partially bedded deposits of See also:gravel, See also:sand and clay, occurring separately or in every conceivable See also:condition of association. Some of these deposits have received distinctive names; such are the " See also:Kames " of Scotland, which are represented in See also:Ireland by " Eskers," and in Scandinavia by " Asar." Another type of hillocky deposit is exemplified by the " drums " or " drumlins." Everywhere beyond the margin of the advancing or retreating ice-sheets these deposits were being formed; streams See also:bore away coarse and See also:fine materials and spread them out upon alluvial plains or upon the floors of innumerable lakes, many of which were directly caused by the damming of the ordinary water-courses by the ice. As the level of such lakes was changed new See also:beach-lines were produced, such as are still evident in the great See also:lake region of North America, in the parallel roads of Glen See also:Roy, and the " Strandlinien " of many parts of northern Europe. Viewed in relation to See also:man's position on the See also:earth, no geological changes have had a more profound importance than those of the Glacial period. The whole of the glaciated region bears evidence of remarkable modification of topographic features; in parts of Scotland or See also:Norway or See also:Canada the old rocks are bared of See also:soil, rounded and smoothed as far as the See also:eye can see. The old soil and subsoil, the product of ages of ordinary weathering, were removed from vast areas to be deposited and concentrated in others. Old valleys were filled—often to a great See also:depth, 300-400 ft.; See also:rivers were diverted from their old courses, never to return; lakes of vast size were caused by the damming of old outlets (Lake Lahontan, Lake See also:Agassiz, &c., in North America), while an See also:infinite number of shifting lakelets—with their deposits —played an important part along the ice-front at all stages of its career. The influence of this period upon the See also:present hardly be overestimated. Much stress has been laid upon supposed great changes in the level of the land in northern regions during the Glacial period. The occurrence of marine shells at an See also:elevation of 1350 ft. at 1VIoel Tryfaen in north See also:Wales, and at 1200 ft. near See also:Macclesfield in See also:Cheshire, has been cited as evidence of profound submergence by some geologists, though others see in these and similar occurrences only the transporting action of ice-sheets that have traversed the floor of the adjoining seas. Marine shells in stratified materials have been found on the See also:coast of Scotland at too ft. and over, in S. Scandinavia at 600 to 800 ft., and in the " See also:Champlain " deposits of North America at various heights. The dead shells of the "Yoldia clay" See also:cover wide areas at the bottom of the North See also:Atlantic at depths from 500 to 1300 fathoms, though the same mollusc is now found living in See also:Arctic seas at the depth of 5 to 15 fathoms. This has been looked upon as a See also:proof that in the N.W. See also:European region the See also:lithosphere stood about 2600 ft. higher than it does now (See also:Brogger, See also:Nansen, &c.), and it has been suggested that a See also:union of the mainland of Europe with that of North America—forming a northern See also:continental mass, " Prosarctis "—may have been achieved by way of See also:Iceland, See also:Jan See also:Mayen Land and See also:Greenland. The pre-glacial valleys and fjords of Norway and Scotland, with their deeply submerged seaward ends, are regarded as proofs of former elevation. The great depth of See also:alluvium in some places (236 metres at See also:Bremen) points in the same direction. Evidences of changes of level occur in early, See also:middle and See also:late Pleistocene formations, and the nature of the evidence is such that it is on the whole safer to assume the existence only of the more moderate degree of See also:change. The Cause of the Glacial Period.—Many attempts have been made to formulate a satisfactory hypothesis that shall conform with the known facts and explain the great change in See also:climatic conditions which 'set in towards the See also:close of the Tertiary era, and culminated during the Glacial period. Some of the more prominent hypotheses may be mentioned, but space will not permit of a detailed See also:analysis of theories, most of which See also:rest upon somewhat unsubstantial ground. The See also:principal facts to be taken into See also:consideration are (1) the great lowering of temperature over the whole earth; (2) the localization of extreme glaciation in north-See also:west Europe and north-See also:east America; and (3) the See also:local retrogression of the ice-sheets, once or more times repeated. Some have suggested the See also:simple See also:solution of a change in the earth's See also:axis, and have indicated that the See also:pole may have travelled through some 150 to 200 of See also:latitude; thus, the polar glaciation, as it now exists,might have been in this way transferred to include north-west Europe and North America; but See also:modern views on the rigidity of the earth's See also:body, together with the lack of any evidence of the correlative movement of climatic zones in other parts of the world, render this hypothesis quite untenable. On similar grounds a change in the earth's centre of gravity is unthinkable. Theories based upon the See also:variations in the obliquity of the See also:ecliptic or eccentricity of the earth's See also:orbit, or on the passage of the See also:solar See also:system through See also:cold regions of space, or upon the known variations in the See also:heat emitted by the See also:sun, are all insecure and unsatisfactory. The hypothesis elaborated by James See also:Croll (Phil. Mag., 1864, 28, p. 121; See also:Climate and Time, 1875; and Discussion on Climate and Cosmology, 188g) was founded upon the assumption that with the earth's eccentricity at its maximum and See also:winter in the north at See also:aphelion, there would be a tendency in northern latitudes for the See also:accumulation of See also:snow and ice, which would be accentuated indirectly by the formation of fogs and a modification of the See also:trade winds. The shifting 6f the thermal See also:equator, and with it the direction of the trade winds, would divert some of the warm ocean currents from the cold regions, and this effect was greatly enhanced, he considered, by the configuration of the Atlantic Ocean. Croll's hypothesis was supported by Sir R. See also:Ball (The Cause of the Great Ice Age, 1893), and it met with very general See also:acceptance; but it has been destructively criticized by Professor S. See also:Newcomb (Phil. distribution of plant and See also:animal See also:life in northern latitudes can Mag., 1876, 1883, 1884) and by E. P. Culverwell (Phil. Mag., 1894, p. 541, and Geol. Mag., 1895, pp. 3 and S5). The difficulties in the way of Croll's theory are: (I) the fundamental assumption, that midwinter and midsummer temperatures are directly proportional to the sun's heat at those periods, is not in accordance with observed facts; (2) the glacial periods would be limited in duration to an appropriate fraction of the precessional period (21,000 years), which appears to be too See also:short a time for the work that was actually done by ice agency; and (3) Croll's glacial periods would alternate between the northern and See also:southern hemispheres, affecting first one then the other. Sir C. Lyell and others have advocated the view that great elevation of the land in polar regions would be conducive to glacial conditions; this is doubtless true, but the evidence that the Glacial period was primarily due to this cause is not well established. Other writers have endeavoured to support the elevation theory by combining with it various astronomical and meteorological agencies. More recently several hypotheses have been advanced to explain the glacial period as the result of changes in the See also:atmosphere; F. W. Harmer (" The Influence of Winds upon the Climate during the Pleistocene See also:Epoch," Q.J.G.S., 19oi, 57, p. 405) has shown the importance of the influence of winds in certain circumstances; See also:Marsden See also:Manson (" The See also:Evolution of Climate," American Geologist, 1899, 24, p. 93) has laid stress upon the influence of clouds; but neither of these theories grapples successfully with the fundamental difficulties. Others again have requisitioned the variability in the amount of the See also:carbon dioxide in the atmosphere—hypotheses which depend upon the efficiency of this See also:gas as a thermal absorbent. The See also:supply of carbon dioxide may be increased from time to time, as by the emanations from volcanoes (S. See also:Arrhenius and A. G. Hogbom), or it may be decreased by absorption into See also:sea-water, and by the carbonation of rocks. Professor T. C. Chamberlin based a theory of glaciation on the depletion of the carbon dioxide of the See also:air (" An See also:Attempt to See also:frame a Working Hypothesis of the cause of Glacial Periods on an Atmospheric Basis," Jl. Geol., 1899, vii. 752-771; see also Chamberlin and See also:Salisbury, Geology, 19(36, ii. 674 and iii. 432). The outline of this hypothesis is as follows: The general conditions for glaciation were (I) that the oceanic circulation was interrupted by the existence of land; (2) that See also:vertical circulation of the atmosphere was accelerated by continental and other influences; (3) that the thermal blanketing of the earth was reduced by a depletion of the moisture and carbon dioxide in the atmosphere, and that hence the See also:average temperature of the See also:surface of the earth and of the body of the ocean was reduced, and diversity in the distribution of heat and moisture introduced. The localization of glaciation is assignable to the two great areas of permanent atmospheric depression that have their present centres near Greenland and the Aleutian Islands respectively. The periodicity of glacial advances and retreats, demanded by those who believe in the validity of so-called " interglacial " epochs, is explained by a See also:series of complicated processes involving the alternate depletion and completion of the normal See also:charge of carbon dioxide in the air. Whatever may be the ultimate See also:verdict upon this difficult subject, it is tolerably clear that no simple cause of glacial conditions is likely to be discovered, but rather it will appear that these conditions resulted from the interaction of a complicated series of factors; and further, until a greater degree of unanimity can be approached in the See also:interpretation of observed facts, particularly as regards the substantiality of interglacial epochs, the very See also:foundations of a See also:sound working hypothesis are wanting. See also:Classification of Glacial Deposits—Interglacial Epochs.—Had the deposits of glaciated regions consisted solely of boulder clay little difficulty might have been experienced in dealing with their classification. But there are intercalated in the boulder See also:clays those irregular stratified and partially stratified masses of sand, gravel and See also:loam, frequently containing marine or See also:freshwater shells and layers of See also:peat with plant remains, which have given rise to the conception of "'interglacial epochs " pauses in the rigorous conditions of glaciation, when the ice-sheets dwindled almost entirely away, while See also:plants and animals re-established themselves on the newly exposed soil. Glacialists may be ranged in two See also:schools: those who believe that one or more phases of milder climatic conditions See also:broke up the whole Glacial period into alternating epochs of glaciation and "de-glaciation "; and those who believe that the intercalated deposits represent rather the localized recessional movements of the ice-sheets within one single period of glaciation. In addition to the stratified deposits and their contents, important evidence in favour of interglacial epochs occurs in the presence of weathered surfaces on the See also:top of older boulder clays, which are themselves covered by younger glacial deposits. The cause of the interglacial hypothesis has been most ardently championed in England by Professor James Geikie; who has endeavoured to show that there were in Europe six distinct glacial epochs within the Glacial period, separated by five epochs of more moderate temperature. These are enumerated below: 6th Glacial epoch, Upper Turbarian, indicated by the deposits of peat which underlie the See also:lower raised beaches. 5th Interglacial epoch, Upper Forestian. 5th Glacial epoch, Lower Turbarian, indicated by peat deposits overlying the lower See also:forest-bed, by the raised beaches and carseclays of Scotland, and in part by the Littorina-clays of Scandinavia. 4th Interglacial epoch, Lower Forestian, the lower forests under peat beds, the Ancylus-beds of the great freshwater Baltic lake and the Littorina-clays of Scandinavia. 4th Glacial epoch, Mecklenburgian, represented by the moraines of the last great Baltic glacier, which reach their southern limit in See also:Mecklenburg; the roo-ft. See also:terrace of Scotland and the Yoldia-beds of Scandinavia. 3rd Interglacial epoch, Neudeckian, intercalations of marine and freshwater deposits in the boulder clays of the southern Baltic coasts. 3rd Glacial epoch, Polandian, glacial and fluvio-glacial formations of the minor Scandinavian ice-sheet; and the " upper boulder clay" of northern and western Europe. 2nd Interglacial epoch, Helvetian, interglacial beds of See also:Britain and lignites of Switzerland. 2nd Glacial epoch, Saxonian, deposits of the period of maximum glaciation when the northern ice-sheet reached the See also:low ground of See also:Saxony, and the Alpine glaciers formed the outermost moraines. 1st Interglacial epoch, Norfolkian, the forest-bed series of See also:Norfolk. 1st Glacial epoch, Scanian, represented only in the See also:south of See also:Sweden, which was overridden by a large Baltic glacier. The Chillesford clay and Weybourne crag of Norfolk and the See also:oldest moraines and fluvio-glacial gravels of the Arctic lands may belong to this epoch. In a similar manner Professor Chamberlin and other American geologists have recognized the following stages in the glaciation of North America: The Champlain, marine substage. The Glacio-lacustrine substage. The later See also:Wisconsin (6th glacial). The fifth interglacial. The earlier Wisconsin (5th glacial). The Peorian (4th interglacial). The Iowan (4th glacial). The Sangamon (3rd interglacial). The Illinoian (3rd glacial). The See also:Yarmouth or See also:Buchanan (2nd interglacial). The Kansan (2nd glacial). The Aftonian (1st interglacial). The sub-Aftonian or Jerseyan (1st glacial). Although it is admitted that no strict correlation of the European and North American stages is possible, it has been suggested that the Aftonian may be the See also:equivalent of the Helvetian; the Kansan may represent the Saxonian; the Iowan, the Polandian; the Jerseyan, the Scanian; the early Wisconsin, the Mecklenburgian. But considering how fragmentary is much of the evidence in favour of these stages both in Europe and America, the value of such attempts at correlation must be infinitesimal. This is the more evident when it is observed that there are other geologists of equal See also:eminence who are unable to accept so large a number of epochs after a close study of the local circumstances; thus, in the sub-joined See also:scheme for north Germany, after H. W. Munthe, there are three glacial and two interglacial epochs. ( The Mya time =See also:beech-time. Post-Glacial epoch - The Littorina time = See also:oak-time. The Ancylus time = See also:pine- and See also:birch-time. Including the upper boulder clay, J " younger Baltic moraine " with the 1 Yoldia or Dryas phase in the retrogressive See also:stage. 2nd Interglacial epoch including the Cyprina-clay. 2nd Glacial epoch, the maximum glaciation. 1st Interglacial epoch. 1st Glacial epoch, " older boulder clay." Again, in the See also:Alps four interglacial epochs have been recognized ; while in England there are many who are willing to concede one such epoch, though even for this the evidence is not enough to satisfy all glacialists (G. W. Lamplugh, Address, See also:Section C, Brit. Assoc., See also:York, 1906). This great diversity of opinion is eloquent of the difficulties of the subject; it is impossible not to see that the See also:discovery of interglacial epochs bears a close relationship to the origin of certain hypotheses of the cause of glaciation; while it is significant that those who have had to do the actual mapping of glacial deposits have usually greater difficulty in finding See also:good evidence of such definite ameliorations of climate, than those who have founded their views upon the examination of numerous but isolated areas. Extent of Glacial Deposits.—From evidence of the kind cited above, it appears that during the glacial period a serieA of great ice-sheets covered enormous areas in North America and north-west Europe. The See also:area covered during the maximum extension of the ice has been reckoned at 20 million square kilometres (nearly 8 million sq. m.) in North America and 62 million square kilometres (about 22 million sq. m.) in Europe. In Europe three great centres existed from which the ice-streams radiated; foremost in importance was the region of Fennoscandia (the name for Scandinavia with See also:Finland as a single geological region) ; from this centre the ice spread out far into Germany and See also:Russia and westward, across the North Sea, to the shores of Britain. The southern boundary of the ice extended from the See also:estuary of the See also:Rhine in an irregular series of lobes along the Schiefergebirge, Harz, Thuringerwald, See also:Erzgebirge and See also:Riesengebirge, and the northern flanks of the Carpathians towards See also:Cracow. Down the valley of the See also:Dnieper a See also:lobe of the ice-sheet projected as far as 400 50' N.; another lobe extended down the See also:Don valley as far as 48° N.; thence the boundary runs north-easterly towards the Urals and the Kara Sea. The See also:British Islands constituted the centre second in importance; Scotland, Ireland and all but the southern part of England were covered by a moving ice-cap. On the west the ice-sheets reached out to sea; on the east they were conterminous with those from Scandinavia. The third European centre was the Alpine region; it is abundantly clear from the masses of morainic detritus and perched blocks that here, in the time of maximum glaciation, the ice-covered area was enormously in excess of the shrivelled remnants, which still remain in the existing glaciers. All the valleys were filled with moving ice; thus the See also:Rhone glacier at its maximum filled Lake See also:Geneva and the See also:plain between the Bernese Oberland and the See also:Jura; it even overrode the latter and advanced towards See also:Besancon. Extensive glaciation was not limited to the aforesaid regions, for all the areas of high ground had their See also:independent glaciers strongly See also:developed; the See also:Pyrenees, the central See also:highlands of See also:France, the See also:Vosges, See also:Black Forest, See also:Apennines and See also:Caucasus were centres of minor but still important glaciation. The greatest expansion of ice-sheets was located on the North American See also:continent; here, too, there were three principal centres of outflow: the " Cordilleran " ice-sheet in the N.W., the " Keewatin " sheet, radiating from the central See also:Canadian plains, and the eastern " Labrador " or " Laurentide " sheet. From each of these centres the ice poured outwards in every direction, but the principal flow in each case was towards the south-west. The southern boundary of the glaciated area runs as an irregular See also:line along the 490 parallel in the western part of the continent, thence it follows the See also:Mississippi valley down to its junction with the See also:Ohio (southern limit 370 30' N.), eastward it follows the direction of that See also:river and turns north-eastward in the direction of New See also:Jersey. As in Europe, the mountainous regions of North America produced their own local glaciers; in the Rockies, the Olympics and Sierras, the Bighorn Mountains of See also:Wyoming, the Uinta Mountains of See also:Utah, &c. Although it was in the northern hemisphere that the most extensive glaciation took See also:place, the effects of a general lowering of temperature seem to have been See also:felt in the mountainous regions of all parts; thus in South America, New See also:Zealand, See also:Australia and See also:Tasmania glaciers reached down the valleys far below the existing limits, and even where none are now to be found. In See also:Asia the evidences of a former extension of glaciation are traceable in the Himalayas, and northward in the high ranges of See also:China and Eastern See also:Siberia. The same is true of parts of See also:Turkestan and See also:Lebanon. I nAf rica also, in British East See also:Africa moraines are discovered 5400 ft. below their modern limit. In Iceland and Greenland, and even in the See also:Antarctic, there appears to be evidence of a former greater extension of the ice. It is of See also:interest to See also:note that See also:Alaska seems to be free from excessive glaciation, and that a remark-able " driftless " area lies in Wisconsin. The maximum glaciation of the Glacial period was clearly centred around the North Atlantic. Glacial Epochs in the Older Geological Periods.—Since Ramsay See also:drew attention to the subject in 1855 (" On the occurrence of angular, subangular, polished and striated fragments and boulders in the See also:Permian See also:Breccia of See also:Shropshire, See also:Worcestershire, &c., and on the probable existence of glaciers and icebergs in the Permian epoch," Q.J.G.S., 1855, pp. 185-205), a good See also:deal of attention has been paid to such formations. It is now generally acknowledged that the Permo-carboniferous conglomerates with striated boulders and polished rock surfaces, such as are found in the Karoo formation of South Africa, the Talkir See also:conglomerate of the See also:Salt Range in See also:India, and the corresponding formations in Australia, represent undeniable 3rd Glacial glacial conditions at that period on the great Indo-Australian continent. A glacial origin has been suggested for numerous other conglomeratic formations, such as the Pre-See also:Cambrian See also:Torridonian of Scotland, and " Geisaschichten " of Norway ; the basal Carboniferous conglomerate of parts of England; the Permian breccias of England and parts of Europe; the Trias of See also:Devonshire; the coarse conglomerates in the Tertiary See also:Flysch in central Europe; and the See also:Miocene conglomerates of the Ligurian Apennines. In regard to the glacial nature of all these formations there is, however, great divergence of opinion (see A. Heim, " Zur Frage der exotischen Blocke in Flysch," Eclogae geologicae Helvetiae, vol. ix. No. 3, 1907, pp. 413-424). (J. A. Additional information and CommentsThere are no comments yet for this article.
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