CHAP. XIII. RE-ELEVATION OF SCOTLAND. 247 



Others have been left strewed over the bottom of the large 

 intervening vale of Strathmore.* 



It may be argued that the transportation of such blocks 

 may have been due not to floating ice, but to a period when 

 Strathmore was filled up with land ice, a current of which ex 

 tended from the Perthshire Highlands to the summit of the 

 Sidlaw Hills, and the total absence of marine or freshwater 

 shells from all deposits, stratified or unstratified, which have 

 any connection with these erratics in Forfarshire and Perth 

 shire may be thought to favour such a theory. 



But the same mode of transport can scarcely be imagined 

 for those fragments of mica-schist, one of them weighing from 

 eight to ten tons, which were observed much farther south 

 by Mr. Maclaren on the Pentland Hills, near Edinburgh, at 

 the height of 1,100 feet above the sea, the nearest mountain 

 composed of this formation being fifty miles distant.! On 

 the same hills, also, at all elevations, stratified gravels occur 

 which, although devoid of shells, it seems hardly possible to 

 refer to any but a marine origin.f 



Although I am willing, therefore, to concede that the 

 glaciation of the Scotch mountains, at elevations exceeding 

 2,000 feet, may be explained by land ice, it seems difficult 

 not to embrace the conclusion that a subsidence took place 

 not merely of 500 or 600 feet, as demonstrated by the 

 marine shells, but to a much greater amount, as shown by the 

 present position of erratics and some patches of stratified drift. 

 The absence of marine shells at greater heights than 525 feet 

 above the sea, will be treated of in a future chapter. It may 

 in part, perhaps, be ascribed to the action of glaciers, which 

 swept out marine strata from all the higher valleys, after 

 the re-emergence of the land. 



* Proceedings of the Geological f Maclaren, Geology of Fife, &c., 

 Society, vol. iii. p. 344. p. 220. 



