GRANITIC AIGUILLES. 



53 



they were raised. As the ocean from which these beds were raised, 

 must have been agitated with inconceivable violence, the retiring wa- 

 ters would scoop out deep excavations in the softer beds of schist, 

 and also tear off many of the vertical plates of the hardest rocks, and 

 form the rudiments of those pyramidal peaks and aiguilles, which 

 rise like the spires of a Gothic cathedral. Mountain torrents, cau- 

 sed by thunder storms or the sudden melting of alpine snow, may 

 have subsequently torn away large portions both of the harder and 

 softer beds : the disintegration of the granitic aiguilles, which are ex- 

 posed to the influence of atmospheric agency, is daily taking place, 

 and their ruins are, every day, falling on the surface of the glaciers, 

 and are carried down into the valleys : their peculiar forms are deri- 

 ved from their laminated structure, which disposes them to split in a 

 vertical direction."^ 



It is important to observe, that different groups and ranges of moun- 

 tains have been elevated, at different and remote epochs, and the birth 

 of different parts of the same continent was not coeval : the more lofty 

 parts constituted separate islands, before the whole surface emerged 

 from the ocean. Satisfactory evidence of this will be adduced in a 

 subsequent part of this work : it is sufficient to the present purpose 

 to state, that the ocean has covered all that is now dry land, but not 

 at the same epoch. 



* Plate n. Fig. 2. represents the general position of the beds near the Col de 

 Balme and Mont Blanc ; a a a, alternatingbeds of sandstone and limestone ; b h, ele- 

 vated beds of puddingstone, containing rounded stones and fragments of the low- 

 er rocks; c c, soft slate, in which a passage or col is formed; ddd, vertical gran- 

 itic beds rising in pyramidal forms, called Aiguilles or Needles. 



