12 ffeESIDENT's ADDRESS. , - 



I paSs oh, therefore, to mention another difficulty in this hypothesis 

 — that the Alpine 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 Penck and 

 Bruckner, since the first great advance of the Alpine ice. One of the 

 latest estimates of the thickness of the several geological formations 

 assigns 4,000 feet ' to the Pleistocene and Eecent, 13,000 to the Pliocene, 

 and 14,000 to the Miocene. If we assume the times of deposit to be pro- 

 portional 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 denudation 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 curve given by Penck and Bruckner, the temperature was below its 

 present amount for rather less than half (0*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 command make it probable that a 

 Norway glacier at the present day lowers its basin by only about 

 80 millimetres in 1,000 years; a Greenland glacier may remove some 

 421 millimetres in the same time, while the Vatnajokul in Iceland 

 attains to 647 millimetres. If Alpine glaciers had been as effective as the 

 last-named, they would not have removed, during their 188,000 years 

 of occupation of the Alpine valleys, more than 121.6 metres, or just 

 over 397 feet; and as this is not half the amount demanded by the more 

 moderate advocates of erosion, we must either ascribe an abnormal 

 activity to the vanished Alpine glaciers, or admit that water was much 

 more effective as an excavator. 



We must not forget that glaciers cannot have been important 

 agents in the sculpture of the Alps during more than part 

 of Pleistocene times. That sculpture probably began in the 

 Oligocene period; for rather early in the next one the great 

 masses of conglomerate, called Nagelfluh, show that powerful rivers 

 had already carved for themselves valleys corresponding generally 

 with and nearly as deep as those still in existence. Temperature 

 during much of the Miocene period was not less than 12° P. above its 

 present average. This would place the snow-line at about 12,000 feet. 3 



1 I have doubts whether this is not too great. 



2 I take the fall of temperature for a rise in altitude as 1° F. for 300 feet or, when 

 the differences in the latter are large, 3° per 1,000 feet. These estimates will, I think, 

 be sufficiently accurate. The figures given by Hann (see for a discussion of the 

 question, Brit. Assoc. Report, 1909, p. 93) work out to 1° F. for each 318 feet of 

 ascent (up to about 10,000 feet). 



