REFEEENCE TO THE ANTIQUITY OE MAN. 



399 



1854 and 1865, or at the rate of about 155 feet annually. The 

 mean annual ablation of the Swiss glaciers is estimated at about 

 10 feet, but on the Glacier des Bossons the surface of the ice has been 

 lowered 260 feet in twelve years. 



Here, then, seasonal fluctuations alone are attended by alternate 

 advances and retreats of the glacier-front of not less, on a mean of 

 these instances, than from 200 to 300 feet per annum. If, then, 

 mere seasonal fluctuations are attended by changes of this extent, 

 it would follow that with the secular increase of cold during the 

 Glacial epoch the rate of progress must have considerably exceeded 

 these limits. Taking for the present a mean rate of 250 feet, the 

 longest of the old Swiss glaciers, namely that of the Rhone, which 

 then had a length of 250 miles, might have travelled that distance in 

 5000 years. This, however, is assuming the absence of seasonal 

 retardations and fluctuations, which is not possible. Allowances 

 have to be made for warmer seasons and temporary retreats of the 

 ice, and also for the fact that the old glacier did not move on the 

 steep inclines of Alpine valleys, but traversed the small incline 

 of a great river-plain. On the other hand, we have to take into 

 account the circumstance that the present seasonal changes give 

 measure of the growth of ice under the continuous and more extreme 

 glacial conditions of that epoch. Nothing positive can therefore 

 be founded on this case, though it may serve to show the possibility 

 of a more rapid rate of progress of the old glaciers than the present 

 estimates allow. 



We have, however, in Arctic regions truer and more adequate 

 terms of comparison in the great ice-sheet of Greenland. Already 

 in 1876 Professor Helland * showed that the Greenland glaciers had 

 a much more rapid rate of flow than those of Switzerland. The 

 Jakobshavn glacier, notwithstanding its small slope of only half 

 a degree, was found to advance its front at the rate of from 50 to 60 

 feet a day. The flow of the glacier of the Fjord of Torsukatak, 

 which is nearly five miles broad, gave a rate of from 12 to 33 feet 

 daily. Taking the average rate of the three glaciers on which 

 Prof. Helland made observations, the average discharge of the ice 

 was 23 feet in twenty-four hours ; and he estimated that at the 

 Jakobshavn glacier only four years would required be to transport 

 a mass from the edge of the inland ice to the sea, a distance of 12| 

 miles. But he considered it improbable that the inland ice would 

 move with anything like the velocity of the glaciers, and calculated 

 that a mass of ice starting halfway between the east and west coasts 

 of Greenland would take eighty-one years to reach the Fjord. 

 These observations were, however, made in the summer months, 

 and were only of a few days' duration, so that the annual rate was 

 not ascertained. 



Since then a Danish scientific expedition, consisting of engineers 

 and geologists (one of whom, Mr. K. J. v. Steenstrup, passed eight 

 summers and two winters in the country), have completed a most 

 important exploration of the Greenland ice, of which a short sum- 



* Quart. Journ. Geol. Soc. vol. xxxiii. p. 142. 



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