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EXPLANATION OF GEOLOGICAL FACTS, 
the consequence of the contraction of a clay base. The schistus 
with these characters has two extremes, one near its junction with 
the granite, the other when most remote from it. Near the granite 
it is distinctly granular to the naked eye ; when most remote it 
passes into slate. The slate which is to be seen in quarries in Lion’s 
Hill is intersected by narrow veins of quartz, and might be taken at 
first sight for primitive clay slate, but is of a dark gray colour, 
and contains scales of mica which, under a strong magnifier, give it 
the appearance of mica slate : it is, however, thus viewed, distinctly 
granular, and more so after exposure to heat. These are the leading- 
characters and gradations of the schistus of the Cape ; I call it 
schistus, because it is always distinctly stratified and has more or 
less of a slaty fracture. 
The theory of the igneous origin of granite adopted by Cap- 
tain Hall and Mr. Playfair to explain the phenomena visible in 
Table Mountain, very happily meets the facts, and must appear, 
I apprehend, to one standing on the spot where they occur, as 
incontestible. * They are indeed of that nature which strikes the 
conviction at the first glance. Carry to the spot one who never 
heard of geological theories, and ask him what he infers from the 
appearances before him, and he will exclaim, “ The white rock has 
broken the black in pieces.” Whatever maybe the true explanation 
of the appearances, this I apprehend must be the first impression 
that affects the mind of any person visiting Table Mountain. A 
* “ The penetration of the killas, or grawacky, by veins from the mass of granite which 
it surrounds, proves that the killas, though the superior rock, is of older formation than 
the granite. The granite, therefore, is a mineral that has come up from below into the 
situation it now occupies, and is not one of which the materials have been deposited by the 
sea in any shape, either mechanical or chemical. It is a species therefore of subterraneous 
lava, and the progeny of that active and powerful element which we know, from the 
history both of the present and the past, has always existed in the bowels of the earth.” 
Account of the Structure of the Table Mountain, and other Parts of the Peninsula at 
the Cape, drawn up by Professor Playfair from Observations by Captain Basil Hall. — 
Edinburgh Philosophical Transactions, vol. 7- 
