Lithological Survey of Schehallien. 577 
that merits particular attention, and is hardly to be looked 
for any where but among granite mountains, as they alone 
afford a perfect security that their interior and exterior are 
composed of the same materials. Granite is the lowest of the 
rocks, and whenever it appears at the surface we may be as- 
sured, that on penetrating deeper, we shall meet with no 
other. 
It is therefore to the primitive mountains, and among them 
to the granitic, that such experiments as those made at Sche- 
hallien ought to be confined. The want of homogeneity will 
then be on the outside of the mountain only, and can easily 
be estimated. The granite may be covered at the bottom of the 
mountain and even to a considerable height on its sides with 
beds of gneiss, mica slate, hornblende slate, &c., the quan- 
tity and position of which can easily be ascertained by obser- 
vation. 
3C 
MDCCCXI. 
