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SCIENCE 



[X. S. Vol. XXXII. No. 819 



first I am unable to discern more than the 

 normal effects of a rather rapid river 

 which has followed a trough of compar- 

 tively soft rocks; in the second, only the 

 cliffs marking the channel cut by a similar 

 stream through massive limestones — cliffs 

 like those which elsewhere rise up the 

 mountain flanks far above the levels 

 reached by glaciers ; while in the third I 

 have failed to discover, after repeated ex- 

 amination, anything abnormal. 



Many lake basins have been ascribed to 

 the erosive action of glaciers. Since the 

 late Sir A. Ramsay advanced this hypoth- 

 esis numbers of lakes in various countries 

 have been carefully investigated and the 

 results published, the most recent of which 

 is the splendid work on the Scottish lochs 

 by Sir J. Murray and Mr. L. Pullar." A 

 contribution to science of the highest value, 

 it has also a deeply pathetic interest, for it 

 is a father's memorial to a much-loved son, 

 F. P. Pullar, who, after taking a most ac- 

 tive part in beginning the investigation, 

 lost his life while saving others from 

 drowning. As the time at my command 

 is limited, and many are acquainted with 

 the literature of the subject, I may be ex- 

 cused from saying more than that even 

 these latest researches have not driven me 

 from the position which I have maintained 

 from the first — namely, that while many 

 tarns in corries and lakelets in other favor- 

 able situations are probably due to excava- 

 tion by ice, as in the mountainous districts 

 of Britain, in Scandinavia, or in the 

 higher parts of the Alps, the difficulty of 

 invoking this agency increases with the 

 size of the basin — as, for example, in the 

 case of Loch Maree or the Lake of Annecy 

 — till it becomes insuperable. Even if Glas 

 Llyn and Llyn Llydaw were the work of 

 a glacier, the rock basins of Gennesaret 



" " Bathymetrieal Survey of the Scottish Fresh- 

 water Lochs," Sir J. Murray and Mr. L. Pullar, 

 1910. 



and the Dead Sea, still more those of the 

 great lakes in North America and in Cen- 

 tral Africa, must be assigned to other 

 causes. 



I pass on, therefore, to mention another 

 difficulty in this hypothesis — that the Al- 

 pine valleys were greatly deepened during 

 the glacial epoch — which has not yet, I 

 think, received sufficient attention. From 

 three to four hundred thousand years have 

 elapsed, according to Penek and Briickner, 

 since the, first great advance of the Alpine 

 ice. One of the latest estimates of the 

 thickness of the several geological forma- 

 tions assigns 4,000 feet^° to the Pleistocene 

 and Recent, 13,000 to the Pliocene, and 

 14,000 to the Miocene. If we assume the 

 times of deposit to be proportional to the 

 thicknesses, and adopt the larger figure for 

 the first-named period, the duration of the 

 Pliocene would be 1,300,000 years, and of 

 the Miocene 1,400,000 years. To estimate 

 the total vertical thickness of rock which 

 has been removed from the Alps by denu- 

 dation is far from easy, but I think 14,000 

 feet would be a liberal allowance, of which 

 about one seventh is assigned to the ice age. 

 But during that age, according to a euirve 

 given by Penck and Briickner, the tempera- 

 ture was below its present amoimt for 

 rather less than half (.47) the time. Hence 

 it follows that, since the sculpture of the 

 Alps must have begun at least as far back 

 as the Miocene period, one seventh of the 

 work has been done by ice in not quite one 

 fifteenth of the time, or its action must be 

 very potent. Such data as are at our com- 

 mand make it probable that a Norway 

 glacier at the present day lowers its basin 

 by only about eighty millimeters in 1,000 

 j'ears; a Greenland glacier may remove 

 some 421 millimeters in the same time, 

 while the Vatnajokul in Iceland attains to 

 647 millimeters. If Alpine glaciers had 



" I have doubts whether this is not too great. 



