ASPECT OF GRANITIC MOUNTAINS. 



59 



Granite occurs in masses of vast thickness, which are commonly, 

 divided, by fissures, into blocks, that approach to rhomboidal or pret- 

 ty regular polyhedral forms. Sometimes a columnar structure may 

 be observed in granitic mountains; in other instances, where the 

 quantity of mica is considerable, granite divides into parallel layers 

 or plates, that have been mistaken for strata. Granite is, occasion- 

 ally, found in globular masses, which are composed of concentric 

 spherical layers, separated by granite of a less compact kind, and en- 

 closing a hard or central nucleus. These globular masses are, often 

 three or four yards, or more, in diameter, and are either detached or 

 imbedded in granite of a softer kind ; this structure is not peculiar to 

 granite. 



The aspect of granitic mountains is extremely various : where the 

 beds are nearly horizontal, or where the granite is soft and disintegra- 

 ting, the summits are rounded, heavy and unpicturesque. Where 

 hard and soft granite are intermixed in the same mountain, the softer 

 granite is disintegrated and falls away, and the harder blocks remain 

 piled in confusion on each other, like an immense mass of ruins. 

 Where the granite is hard, and the beds are nearly vertical, and have 

 a laminar structure, it forms lofty pyramidal peaks or aiguilles, that 

 rise in enormous spires; such are the aiguilles in the vicinity of Mont 

 Blanc, which are far more interesting, both to the picturesque travel- 

 ler or the geologist, than Mont Blanc itself. The Aiguille de Dru is 

 perhaps, the most remarkable graninc mountain at present known ; 

 the upper part or spire, rises above its base nearly to a point in one 

 solid shaft more than four thousand feet ; the summit is eleven thou- 

 sand feet above the level of the sea.^ 



It has been observed in so many situations, that it may perhaps be 

 regarded as a general law, — wherever granite rises high above 

 the surface of the earth, the strata of limestone or other rocks 

 in its vicinity rise towards it. Numerous instances of this occur 

 in the Swiss Alps. In the higher part of the valley of Lauter- 

 brun, in the Canton of Berne, I have seen a bed of limestone in im- 

 mediate junction with granite, in a perfectly vertical position, like a 

 wall built up against it; but both rocks were cemented together with- 

 out any perceptible line of parting. The limestone was extremely 

 hard, but the parts in immediate contact with the granite did not dif- 

 fer in appearance from the other parts of the bed. 



In many of the highest mountains in the northern or Swiss Alps, 

 granite is seen only near their bases; the summits are composed of 

 immense beds of limestone, and secondary stratified rocks. In the 

 southern chain, or the Savoy Alps, the highest summits are granite ; 

 indeed, the highest known point at which granite has been observed, 

 in any part of the world, is Mont Blanc in Savoy, the loftiest moun- 



* A short description of this mountain, with a plate, is given in the 2nd Vol. of 

 Travels," by the author. 



