171. 



KNOWLEDGE 



[August, 1902. 



ever, even of Germau orifjin. They prove, as was fairly 

 recognised a century ago, to belong to Scandinavian 

 masses; practically, they liavo been spread across the laud 

 from Sweden. Far from being a jiroduet of the waste of 

 Central Europe, as one would suppose from the present 

 direction of the rivers on its surface, the ]>lain represents 

 the filling up of a depression by the ll<iw of material from 

 the north. How has this material crossed the Baltic, and 

 formed, as it were, a widely stretching delta abutting on 

 Saxony and Bohemia? Surely the deposition should have 

 tjiken place where the Scandinavian streams meet the sea, 

 and not against the opposite shore ? 



Setting aside some early views, which maintained that 

 the boulders were volcanic bombs showered out from 

 seething caldri>ns in the north, geologists were led to 

 believe that flood-waters had swept down fi'om Scandinavia; 

 and, later on, it seemed still more easy to account for the 

 drifted material by the agency of floating ice. This ex- 

 planation would require the submergence of the whole 

 Prussian area in glacial times beneath an extended Baltic 

 sea, the existence of which is at least dubious. At the 

 same time, it leaves the long eskers and other features un- 

 accounted for. The intercalations of marine layers among 

 the " drift " deposits of North Germany are, however, 

 sufficiently numerous to make one regard the area as once 

 occupied by shallow bays and inlets on a shore formed of 

 glacial accumulations. As the ice spread from the north, 

 the earlier deposits were overridden, and no further marine 

 beds could be laid down until the glaciers again retreated. 

 As the ice melted, the burden of stones and sand, largely 

 carried within its mass, became added to the drift and 

 obscured much that had gone before. Making every 

 allowance for the loss of some marine deposits and the 

 effectual concealment of others, it seems, nowadays, 

 impossible to maintain the view that the drift of North 

 Germany, as a whole, was deposited by floating ice. At 

 one time or another, solid ice, highly charged with Scan- 

 dinavian dehris, seems to have spread across the whole 

 Baltic region and far towards the central European high- 

 lands. Prof. James Geikie's map* represents the extreme 

 position reached by certain glacialists, and is enough 

 to arouse criticism, and to make the supporters of the 

 marine view seek for loose rivets in his armour. Dr. 

 Scharff,f who enters the lists against him, does so mainlv 

 on climatic grounds, and m-ges that certain species of the 

 European fauna have survived (in Ireland, for example) 

 from Pliocene times onward, and that no ice-invasion has 

 occurred over Northern Europe sufficient to crush out 

 animal and vegetable life. He is thus led to regard the 

 German drift as a marine deposit, and tlie Irish and British 

 glaciers as local phenomena. Neither Dr. Scharff nor the 

 believers in the frequently recuiring warmer " inter-glacial" 

 epochs seem to make sufficient use of the well-known 

 Malaspina glacier of Alaska,^ which spreads out on almost 

 level groimd, moving and melting so slowly that abundant 

 vegetable and anmial life finds a ])lace upon its surface. 

 It is well to remark, however, that modern observations in 

 high latitudes agree in showing us beds of glacial drift 

 deposited in shallow seas, and subsequently lifted above 

 the water ; the Chaix Hills of Alaska are among the most 

 conspicuous examples, and reach 3000 feet in height. 

 Hence both the advocates of continental ice-sheets and 

 those who invoke the sea may find support when they 

 study "existing causes of change." It is not difficult in 



*"The Great Ice Age," ed. 3 (1891). PL IX., p. 437. 



t" On the Origin of the European Fauna," Proc R. Irish Acad., 

 Ser. 3, A^ol. IV. (1897), pp. 48S -502. Also " Tlie History of 

 the European Fauna," Contemp. Sd. Series (1899), pp. SO— Stj. 



I Thirteenth Ann. Rep. U.S. Oeol. Survey (1892), pp. 19, 26, and 

 67; see also K.nowlebob, Vol. XXI. (1898)', p. 219. 



this controversy to suggest the golden mean ; whatever the 

 former elevation both of Scandinavia and Central Europe 

 may have been in early glacial times, it is clear that the 

 floor upon which the ice oozed forth was swaying slowly 

 up and down somewhere near the level of the sea. 



When we learn that the rock-floor, which is generally 

 hidden in this area, bears on it the grooves and striations 

 first noted by De Saussure, and now so universally asso- 

 ciated with the passage of glacier-ice, we must incline 

 strongly towards the view that ice-sheets have occupied the 

 plain. Dr. WahnschafiEe,* to whose work the present 

 article is so greatly indebted, shows on a map how glacial 

 striiB have been again and again found on rock-surfaces, 

 under the covering of " drift," even so far south as 

 Saxony. Some local glaciers from the Erzgebirge have 

 naturally to be considered when we get into the Dresden 

 area ; but the general conclusion of German geologists at 

 the present day is that the Scandinavian ice spread, at one 

 time or another, as a vast sheet over the whole Prussian 

 plain, and deposited its boulders at heights of 415 metres 

 on the Saxon foothills, and even at 42i5 metres in the 

 Riesengebirge to the east.f The exact figures, however, 

 give us little idea of the thickness of the ice or of the 

 slope over which it moved, seeing how many oscillations 

 the plain of Germany has undergone, in company with the 

 mountain-masses to the north. 



If we seek for evidence of these oscillations, and of their 

 impressive magnitude, we may find it in the recent 

 researches of Prof. W. C. Br6gger,J who urges that con- 

 siderable submergence took place even while the ice was 

 melting from the margin of southern Norway. The ice- 

 rim thus dropped its burden of sand and boulders§ into a 

 sea in which boreal, but not necessarily arctic, molluscs 

 lived ; and here again, as is so often recorded, stratified 

 shell-bearing gravels result, of marine yet at the same 

 time glacial origin. These, by the last emergence, are now 

 lifted high and ' dry upon the coast -lands. But beneath 

 them the distinctly striated rock-floor stretches seaward, 

 showing that continuous ice occupied the place of the sea 

 in still earlier times, banking it out from the land, or 

 moving over dry ground when Scandinavia was more 

 elevated than now. All these considerations must weigh 

 with us when we set out across the Prussian plain. 

 Broadly, then, we may feel that certain later deposits should 

 be regarded as submarine stratified moraines ; yet we can- 

 not overlook the preponderating evidence that a huge 

 confluent glacier-fan once spread across the country. 



The phrase moraine profonde, applied to the deposits 

 that come to light on the melting of an ice-sheet, has 

 received different meanings during different stages of 

 research. At one time it was presumed by extreme 

 " glacialists " that boulder-clay was at one and the same 

 time accumulated and thrust forward under the ice 

 itself, as a sort of product of the rasping away of the 

 country over which it moved. Modem observation on 

 existing ice-sheets convinces us that the quantity of 

 material which may be carried in the body of the ice, ap- 

 pearing as the mass melts, and becoming stratified by the 

 accompanying wash of water, is quite sufficient to account 

 for boulder-clays and other drift deposits. Such beds 

 have thus a dual origin, and their final disposition is due 

 more to water than to ice. Probably the moraine profonde 

 of modern authors must be interpreted as this euglacial 



• Op. fit., Plate 2, p. 91. 



+ See Jas. iicikie, " Great Ice Age," ed. 3, p. 438. 



X " Om de senglaoiale og postglacialenivaforandringer i Kristiaais- 

 feltet," Norges geol. undersoqelse, No. 31 (1901), p. 690 (English 

 Summarj). 



§ Ibid., pp. 687 and 689. 



