1893.] evidence for the Recurrence of Ice Ages. 109 



prove the existence of glacial conditions during the deposition of 

 the beds in which they occur. 



Where we might expect to find traces of glacial action is of 

 course where we have evidence of submerged mountain lands, that 

 is at the base of each great system as defined on the table of strata 

 which I laid before the Society on a former occasion \ 



When the sea crept up the pre-Cambrian highlands it must 

 have washed into its depths whatever there was of moraine matter. 

 When the great subsidence commenced that made room for the 

 accumulation of the Carboniferous deposits, the boulders of Silurian, 

 Cambrian and older rocks must have been buried where they were 

 or been swept into the hollows and valleys of the submerged land. 

 When the Carboniferous rocks had been uplifted and acted upon 

 through long ages by all the denuding forces that then as now 

 struggled to reduce the dry land as soon as raised, depression 

 again set in and the land with all its mountain ranges and coast 

 lines again went down ; if there were glaciers here we should find 

 their traces. It is likely there were glaciers somewhere and at 

 these horizons we should still search for evidence. But the 

 question now before us is what is the value of the evidence which 

 has been adduced in favour of that discovery having been already 

 made. 



ix. Southern extension of ice in glacial period. 



The extension of the glacial drift in Southern Germany, 

 suggested by the transport of fragments far from the parent rock, 

 has been supposed to be confirmed especially by the occurrence 

 in the widespread gravel and sand of that area of certain faceted 

 and polished stones. See Nos. QQ, 67. These are composed of 

 very hard material being generally quartzite, and the manner in 

 which they are supposed to have assumed their peculiar form is 

 by having been held in the ice as in a vice and having one face 

 after another ground down as they shifted their position in the 

 mass. Even if the facets were perfectly flat we need some expla- 

 nation of the fact that although there has been such tremendous 

 glacial abrasion there are no glacial striae. But the faces are not 

 fiat and the surface of the portions fretted into hollows are in 

 exactly the same condition as the parts in relief In fact these spe- 

 cimens show none of the essential characters of glacially dressed 

 stones. If however we look back through our collection of variously 

 abraded stones (see p. 102) we shall find that there are some, of which 

 we know the origin, in which the very same characteristics appear as 

 those which distinguish the supposed glacial boulders of Copitz by 

 Pirna. In the sand-worn stones of Cook's Straits, Nos. 18, 19, and 



1 Proc. Camh. Phil. Soc, Vol. iii. p. 247. Brit. Assoc, Eept. 1875. Trans. 

 Sects., p. 70. 



