304 
EXPLANATION OF GEOLOGICAL FACTS, 
immediate vicinity, under equal or greater exposure, has suffered no 
decomposition. 
That “ the decomposition occurred before the deposition of the 
great sandstone formation,” is the necessary consequence of the first 
conclusion; for if the sandstone was deposited on the granite before the 
decomposition of its constituents, whence could that decomposition 
subsequently arise ; how especially could crystals of quartz become 
_ rounded, and how can be explained the . formation of the conglo- 
merate ? The appearance indeed speaks for itself ; it is self-evident 
that the surface of the granite was in a decomposed and disintegrated 
state, when its constituents mixed up with dark red sandstone. 
But if this decomposition and disintegration of the rocks hap- 
pened before the deposition of the sandstone, the hypothesis of 
Capt. Hall and Mr. Playfair*, that the sandstone was deposited 
upon the granite whilst at the bottom of the sea, and that it was 
subsequently raised in so gradual a manner as to have kept its 
relative situation with respect to the rocks on which it rests, can 
scarcely be admitted. For the granite, according to this supposition, 
must have been at that great depth, at which it belongs to no theory 
to suppose that such changes on the surfaces of rocks can occur. On 
the other hand, they are precisely those which we continually see 
rocks undergoing that are exposed to the weather and the action of 
torrents. Therefore the third conclusion respecting the appearances 
I have described may perhaps be safely drawn ; namely, that the 
decomposition and disintegration of the granite occurred “ when 
its surface formed, to a greater or less extent, the surface of the 
earth.” And from this a necessary corollary follows ; that the sand- 
* “ The introduction of the granite into the situation it now occupies must have taken 
place while the whole was deep under the level of the sea : this is evident from the cover- 
ing of sandstone which lies on the granite to the thickness of 1500 feet; for there can be 
no doubt whatever that this last was deposited by water. After this deposition the whole 
must have been lifted up, as Capt. Hall supposes, with such quietness and regularity, and 
in so great a body, as not to disturb or alter the relative position of the parts.” Account 
of the Structure of the Table Mountain in the Edinburgh Philosophical Transactions. 
