GRANITE. 
425 
we observe scattered about in the stone are the mica; 
the two other essential parts, that is, the quartz 
and felt-spar, are blended together to complete the 
composition. 
It appears that granite is the most antient of all 
the rocks, and that it forms the interior part of the 
terrestrial globe, at least to a greater depth than we 
have yet been able to penetrate. This has been 
proved from observation in all the countries of the 
earth ; for granite has ever been found to support 
the superincumbent strata, and has constantly been 
met with when every other substance has been 
penetrated. In the common granite, or that which 
we are at present describing, and which is by far 
the most general, the quartz and felt-spar are mixed 
nearly in an equal quantity, and the mica forms 
about the tenth part of the whole mass. When the 
component parts of the stone are united in this pro- 
portion, it forms the most durable granite, which 
suffers but little alteration from the action of the 
air: if, however, the mica is more abundant, the 
stone will be more subject to decomposition, and 
consequently not so lasting. Striking examples of 
what we have here advanced are noticed by Saus- 
sure. This gentleman tells us that in Lyonnois, in 
Auvergne, in Gevaudan, and in the Vosges, there 
are many places where the earth is composed en- 
tirely of coarse sand, produced by the decomposition 
of granite, which may be said to form the basis of 
these provinces. This circumstance is very rarely 
