206 



SIGNS OF ICE-ACTION IN TERTIARY TIMES. 



[Ch. X. 



who has so successfully devoted much, time and thought to 

 the search for indications of glacial action in remote eras 

 reminds us that a geologist must expect to encounter great 

 difficulties in such investigations. If, at some future era 

 when large portions of the existing continents shall have 

 been submerged and overspread with marine strata, and 

 other parts of them destroyed by denudation, we should have 

 the task assigned to us of detecting those spots where ancient 



of rock had escaped destruction, or where erratic 



surfaces 



moraines 



despair of success. It rarely happens that we have oppor- 

 tunities of examining terrestrial surfaces of high antiquity, 

 and when visible, their extent is always very limited. In the 

 majority of cases they will consist of rocks incapable of re- 

 ceiving and preserving a glacial polish and striation. The 

 least evanescent of the proofs of ice-action which our era is 

 likely to transmit to future ages are, unquestionably, those large 

 angular erratics which have been carried to great distances 

 from their parent rocks ; and wherever such masses occur in 

 older strata they deserve particular attention. I shall pro- 



formation of Miocene 



m 



m 



account for their transportation by any cause other than the 

 buoyant power of ice. 



The marine strata alluded to consist of strata of sandstone 

 and conglomerate, and constitute a member of the Miocene 

 formation of the Collina of Turin, a chain of hills in the 

 suburbs of the capital of Piedmont, on the brow of which 

 stands the church of the Superga. These strata have long 

 been celebrated for containing a plentiful store of fossil shells 

 of the same species as those of the faluns of Touraine, Bor- 

 deaux, and Yienna. The annexed diagram will give the 

 reader some idea of the position of this conglomerate (&), 

 which is highly inclined and conformable to the other strata 

 which dip on each side to the north-west and south-east from 

 the axis of the chain. I examined the district in 1857, in 

 company with Signor Gastaldi, one of the ablest of the Italian 

 geologists, and well versed in glacial phenomena. 



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