286 Dr. J. Croll on the Cause of 



siderable extent, containing boulders, are to be found in the 

 polar tracts previous to the middle of the Tertiary period. 

 Both an examination of the geognostic condition and an 

 investigation of the fossil flora and fauna of the polar lands, 

 show no signs of a glacial era having existed in those parts 

 before the termination of the Miocene period "*. That "Prof. 

 Nordenskjold may not have seen in those strata boulders 

 larger than a child's head may be perfectly true, but that 

 there actually are none is a thing utterly incredible. Still 

 more incredible, however, is the conclusion which he draws 

 from this absence of boulders, viz. that from the Silurian down 

 to the termination of the Miocene period no glacial condition 

 of things existed either in Greenland or in Spitsbergen. 

 Both these places are at present in a state of glaciation ; and 

 were it not, as we have seen, for the enormous quantity of 

 heat which is being transferred from the equatorial regions 

 by the Gulf-stream, not only Greenland and Spitzbergen, 

 but the whole of the Arctic regions would be far more 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 combination 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 im- 

 probable 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 phy- 

 sically impossible, as that the interior of that continent should 

 at the present day be free from ice and covered with luxuriant 

 vegetation. Perhaps the same skill and indomitable perse- 

 verance which proved the one conclusion to be erroneous may 

 yet one day prove the other to be also equally erroneous. 



Professor Nordenskjold does not appear to believe in 

 alternations of climate even in temperate regions, for he 

 says, " from paloeontological science no support can be ob- 

 tained for the assumption of a periodical alternation of warm 

 and cold climates on the surface of the earth." 



Evidence of Glaciation during the Tertiary Period. — 

 Evidence of glaciation during the Miocene period is, I 

 think, afforded by the well-known conglomerates and erratics 

 near Turin, first described by M. Gastaldi. Beds of Miocene 

 sandstone and conglomerate, with an intercalated deposit 

 containing large angular blocks of greenstone and limestone, 

 * ' Geological Magazine/ 1875, p. 531. 





