558 BEPORT— 1889. 



tliis is fully discussed.* These geologists do not deny that some of the material 

 may occasionally have come from above, nor do they doubt that pre-existing 

 masses of rock-rubbish and alluvial accumulations may have been incorporated 

 with the ground-moraines ; but the enormous extent of the latter, and the direction 

 of transport and distribution of the erratics which they contain cannot be thus 

 accounted for, while all tbe facts are readily explained by the action of the ice 

 itself, which used its subglacial debris as tools with which to carry on the work of 

 erosion. 



Professor Heim and others have frequently asserted that glaciers have little or 

 no eroding power, since at the lower ends of existing glaciers we find no evidence 

 of such erosion being in operation. But the chief work of a glacier cannot be 

 carried on at its lower end, where motion is reduced to a minimum, and where the 

 ice is perforated by sub-glacial tunnels and arches, underneath which no glacial 

 erosion can possibly take place ; and yet it is upon observations made in just such 

 places that the principal arguments against the erosive action of glaciers have been 

 based. If all that we could ever know of glacial action were confined to what we 

 can learn from peering into the grottoes at the terminal fronts of existing glaciers, 

 we should indeed come to the conclusion that glaciers do not erode their rocky beds 

 to any appreciable extent. But as we do not look for the strongest evidence of 

 fluviatile erosion at the mouth of a river, but in its valley- and mountain- tracks, so 

 if we wish to learn what glacier-ice can accomplish we must study in detail some 

 wide region from which the ice has completely disappeared. When this plan has 

 been followed, it has happened that some of the strongest opponents of glacial 

 erosion have been compelled by the force of the evidence to go over to the other 

 camp. Dr. Blaas, for example, has been led by his observations on the glacial for- 

 mations of the Inn valley to recant his former views, and to become a formidable 

 advocate of the very theory which he formerly opposed. To his work and the 

 memoirs by Penck, Briickner, and Bohm already cited, and especially to the ad- 

 mirable chapter on glacier-erosion by the last-named author, I would refer those 

 who may be anxious to know the last word on this much-debated question. 



The evidence of interglacial conditions within the Alpine lands continues to 

 increase. These are represented by alluvial deposits of silt, sand, gravel, conglome- 

 rate, breccia, and lignites. Penck, Bohm, and Bruckner find evidence of two 

 interglacial epochs, and maintain that there have been three distinct and separate 

 epochs of glaciation in the Alps. No mere temporary retreat and re-advance of 

 the glaciers, according to them, will account for the phenomena presented by the 

 interglacial deposits and associated moraiuic accumulations. During interglacial 

 times the glaciers disappeared from the lower valleys of the Alps — the climate was 

 temperate, and probably the snow-fields and glaciers approximated in extent to 

 those of the present day. All the evidence conspires to show that an interglacial 

 epoch was of prolonged duration. Dr. Briickner has observed that the moraines of 

 the last glacial epoch rest here and there upon liiss, and he confirms Penck's 

 observations in South Bavaria that this remarkable formation never overlies the 

 morainic accumulations of the latest glacial epoch. According to Penck and 

 Briickner, therefore, the loss is of interglacial age. There can be little doubt, 

 however, that loss does not belong to any one particular horizon. Wahnschaffe ^ 

 and others have shown that throughout wide areas in North Germany it is the 

 equivalent in age of the ' Upper Diluvium,' while Schumacher ^ points out that in 

 the Rhine valley it occurs on two separate and distinct horizons. Professor Andreae 

 has likewise shown* that there are an upper and lower loss in Alsace — each charac- 

 terised by its own special fauna. 



There is still considerable difference of opinion as to the mode of formation of 



' Penck: Die Vergletscherung der deutschen Alpen. Blaas: Zeitsch. d. Ferdinan' 

 deums, 1885. Bohm : Jahrb. d. k. li.. geol. Reichsanstalt, 1885, Bd. xsxv., Heft 3. 

 Bruckner: Die Vergletschervng d. Salzachgehletes, &c., 1886. 



2 Ahhandl. z. geol. SpeciaVkarte v. Pre%issen, &c., Bd. vii. Heft 1 ; Zcitsohr. d. 

 devtsch. geol. Qesellsch., 1885, p. 904 ; 1886, p. 367. 



' Hygienische TopograpMe von Strassburg i. E., 1 885. 



* Abhandl. z. geol. Specialkarte v. Ulsass-Lothriiigen, Bd. vii.. Heft 2. 



