PERCHED BL0CE:S AND ASSOCIATED PHENOMENA. 539 



that there is no foundation for the assumption of extreme dates. He 

 agreed with the Author that these blocks were the results of the 

 last pushing of the ice, having been dropped during the last glacial 

 phase. 



The Atjthoe in reply said the reason why he objected to any 

 numerical estimate of the time which had elapsed since the boulders 

 were left on the glaciated surface was that we knew the rate of 

 weathering in the limestone was most unequal. He gave cases 

 from Devonshire and the Lake-district of extensive weathering in a 

 few years. He had called attention to the great acceleration of 

 decomposition where the vegetation encroached on the limestone, 

 and he maintained that we had no constant measure to apply. 



