The Glacial Theory. 



great mass of the blocks was necessarily buried under the ice, and 

 was therefore subjected to all the effects of a gradual and long- con- 

 tinued trituration, just as is observed beneath the glaciers of the pre- 

 sent day. Mountains of considerable elevation in Scotland — Schi- 

 hallien, for example — ^have their summits as polished as their flanks ; 

 whereas in Switzerland there exists a limit, at about 9000 feet,* in 

 the centre of the Alps, above which the summits are no longer po- 

 lished, but where the rugged peaks present a very striking contrast 

 to the lower surfaces, which are polished, or at least moutonn4s.\ 

 In the exterior chains of the Alps, the polishing does not reach to a 

 greater height than 6000 or 7000 feet. It cannot be doubted, that 

 this limit, which is so well marked, indicates the level of the bed of 

 ice at the epoch of its greatest thickness. The rugged peaks, which 

 exceed that height, thus rose like islets in the midst of this sea of 

 ice, and the blocks which were detached from them fell on the sur- 

 face. Not being confined in narrow valleys, but the whole vast sea 

 of ice being open to them, these blocks were not liable to be knocked 

 against one another in their progress towards the lower districts, and 

 it is thus that they could be transported as far as the Jura, with 

 their surfaces rough and their angles prominent ; whereas, the mat- 

 ters which were beneath the ice, were triturated, polished, rounded, 

 and scratched. Now, if in Switzerland, the limit of the great mass 

 of ice extended as high as 9000 feet in the Alps, and if it oscillated 

 between 4000 and 5000 feet in the Jura which no longer presents 

 glaciers, what is more natural than to admit, taking into account the 

 geographical portion of the localities, that, in Scotland, the great 

 proportion, if not the whole, of the surface, was entirely under ice 

 during the whole duration of the glacial epoch. Hence the majority 

 of the detached blocks of the Scotch mountains must have been 

 transported under the ice, and consequently rubbed, rounded, polish- 

 ed, and scratched. I say the majority, for it is probable that some 

 were detached when the ridges were free from ice, and when the 

 valleys alone were occupied by glaciers; and these latter have ne- 

 cessarily remained more or less angular, and have retained their 



* Ali the measurements given in this paper are in pieds de Roi, or French feet ; and the 

 temperatures are all indicated in centigrade degrees, unless where other measurements or 

 other degrees are specially mentioned. 



t Vide the Compts Rendus de 1' Academic des Science, 1842; tome 14, p. 412. 



