208 Structure of Granitic Mountains. [April, 



however, although the thick laminated structure prevails as in 

 the Brocken, still the matter composing the granitic beds can be 

 proved to have been forced in many instances through narrow 

 fissures in some other rock; which fact seems to us to prove that 

 there was an approach at least to a strictly fluid condition. The 

 great granite quarries of Maine, and many of the thick granitic 

 masses of Massachusetts, rest upon gneiss or mica slate; and it is 

 through rents in those inferior rocks, which are sometimes not 

 over six inches in width, that the granite has been forced in its 

 liquid or semi-liquid state. 



Another result follows from the concentric lamination of grani- 

 tic mountains: the surface is always covered with immense blocks 

 of the material. Situated as those peaks usually are, in a high, 

 frosty region, the laminated masses break up and become dis- 

 membered by the congelation of water confined between the 

 masses. This, together with the rapid process of disintegration 

 which always goes on in the higher regions, separates farther and 

 farther the dismembered rocks, so that in the end, the surface 

 looks as if it was mechanically strewed with blocks of granite, 

 some leaning, some upright, others upon their broad bases, but 

 little removed from their original position; w^hile others are 

 poised upon a projecting point, just ready to be precipitated from 

 their support and roll down the steep. The mountains of New 

 York, particularly the Adirondacks, are in the state and condition 

 we have described. The layers of granite lie parallel to the 

 mountain sides, or nearly so, and might be mistaken for stratifi- 

 cation by one untutored in geological principles, and thus wher- 

 ever there is a flat surface where loose blocks of rock can repose, 

 there we find the accumulations we have spoken of above. Some 

 might entertain the view at first that those loose rocks, inasmuch 

 as they are frequently rounded, that they belonged to the erratic 

 block group of De La Beche; but an examination of the condi- 

 tion and character of the rocks and strata would soon determine 

 the fact that the loose materials belong mostly to the rocks upon 

 which they rest — and that they have been separated from the 

 parent rock by the slow process of frosts and disintegration. 



