AT THE CAPE OF GOOD HOPE. 
297 
ations. I shall now, however, venture to state the explanation 
which occurred to me of some of the principal phenomena ; in doing 
which I shall be found to coincide in inferences already drawn from 
the same class of facts. I may previously remark, that the same 
structure which is found to belong to the mountains accessible from 
their immediate vicinity to Cape Town, in all probability charac- 
terizes those of the great ranges of Southern Africa. In an excursion 
to a ridge of mountains, called the Jungerhook, about forty miles 
north of Cape Town, I found the same general constituents of sand- 
stone, granite, and schistus, entering into their composition, wherever 
I could examine them closely; and I saw no mountain whose summit 
was not formed of horizontally stratified sandstone, and whose base 
was not covered with fragments of schistus and granite. The 
observations of Barrow and other travellers also show, that the 
general structure of the mountains in the interior of Southern Africa 
is the same as that of those in the neighbourhood of Cape Town. 
My description of the appearances in Table Mountain will be 
found to agree in most respects with that of Captain Basil Hall, 
published and reasoned upon by Mr. Playfair in the seventh volume 
of the Edinburgh Philosophical Transactions. The black rock 
which I have called schistus, is there indifferently denominated 
killas and grawacky. Without attempting, to give it a definite appel- 
lation, I shall describe such of its characters as I have been able to 
determine. The Devil’s Hill, which is distinctly stratified, affords, 
perhaps, the best specimens for ascertaining its nature ; as this 
mountain is intermediate between a coarse-grained rock on the one 
hand, and slate on the other. The colour of the rock is a smoke 
gray, with a reddish tint, which becomes deeper in proportion as the 
rock is exposed to the weather. To the naked eye the rock has a 
very fine granular appearance, with a glimmering lustre arising from 
minute scales of mica. Under a lens a sandstone structure becomes 
more distinct, and when the rock has been subjected to the heat 
of a common stove, the quartz sand becomes predominant and 
the conglomerate character unquestionable : this effect is probably 
Q 0. 
