J. Oroll — Evidence of former Glacial Periods. 69 



bat such blocks are seldom, if ever, on the surface of an ice- 

 sheet. The reason is obvious. When a country is completely 

 buried under ice there is no source from which the ice can 

 obtain erratics on its surface. The stones which lie under the 

 ice, before they can reach the sea, are ground down to powder. 

 Large erratic blocks have never been found, for example, on 

 the ice-sheet of Greenland. No one, of course, has as yet had 

 an opportunity of examining the surface of the Antarctic ice, 

 but judging from the character of the icebergs derived from it, 

 we are almost certain that it contains no bowlders. Were the 

 seas surrounding these continents elevated into dry land, a 

 geologist judging from the comparative absence of bowlders in 

 the sedimentary deposits which have been forming for the past 

 thousands of years, would be apt to conclude that these con- 

 tinents had never been covered by ice. In fact, a conclusion 

 of this kind has been arrived at by Professor Norclenskjold, 

 who maintains, because he has never seen in the strata of 

 Greenland or Spitzbergen a bowlder larger than a child's head, 

 that down to the termination of the Miocene period, no glacial 

 condition of things existed in these regions : a conclusion most 

 certainly utterly erroneous. Now both of these lands are at 

 present in a state of glaciation ; and were it not for the enor- 

 mous quantity of heat which is constantly carried northward 

 from the equatorial regions by the Gulf Stream, not only 

 Greenland and Spitzbergen, but the whole of the Arctic 

 regions would be far more completely under ice than they are. 

 A glacial state of things is the normal condition of polar 

 regions ; and if at any time, as during the Tertiary age, the 

 Arctic regions were free from snow and ice, it could only be 

 in consequence of some peculiar distribution of land and water 

 and other exceptional conditions. That this peculiar combina- 

 tion of circumstances should have existed during the whole of 

 that immense lapse of time between the Silurian and the close 

 of the Tertiary period is certainly improbable in the highest 

 degree. In short, that Greenland during the whole of that 

 time should have been free from snow and ice is as improbable, 

 although perhaps not so physically impossible, as that the 

 interior of that continent should at the present day be free 

 from ice and covered with luxuriant vegetation. 



In fact, it is the severity of glacial conditions in these re- 

 gions during glacial periods that has rendered the strata to 

 which Prof. Nordenskjold refers so comparatively free from 

 erratic blocks. Had these regions been occupied by glaciers 

 reaching to the sea, instead of being covered by a sheet of ice, 

 bowlders in the strata would no doubt have been far more 

 common. 



As evidence of former glacial periods we may, however, ex- 



