421 
and Constantia is derived from the decomposition of the granite; and 
the clay of which it consists is either overlaid or contains a hard 
layer consisting of quartz pebbles and ferruginous matter. Mr. Clarke 
does not class this clay, occasionally 100 feet thick, with modern or 
recent formations, because it occurs at the Lion’s Head in gullies, 
whither it could have been transported only by causes no longer in 
operation ; it is moreover everywhere covered with enormous blocks 
of sandstone, and occasionally of granite, but is not mingled with 
them, except at the Kloof, and in the beds of the excavating tor- 
rents; he is therefore of opinion that it was accumulated during the 
period when the whole mass of granite lay beneath the waters of 
the sea. 
The sandstone which enters so largely into the geological consti- 
tution of the Cape district, and forms the upper part of Table Moun- 
tam, has not yet yielded any organic remains; but in a very similar 
sandstone, resting upon granite, at Cedar Berg and other parts of 
the colony, true Silurian Trilobites, with other fossils of that age, 
have been found*. ‘The Cape sandstone is stated to resemble in 
- mineral character the Caradoc more than the old or new red sand- 
stone, and the altered portions are said to be closely analogous in 
appearance to the Lickey quartz rock. Many of the beds are soft 
and white; others are hard, dark-coloured, and very ferruginous ; 
and some are composed of a quartzose conglomerate. Large hol- 
lows or excavations, such as exist where the sea beats against a 
sandstone cliff, appear in all the sandstone escarpments, plainly show- 
ing, Mr. Clarke observes, that the sandstone of Table Mountain was 
once a cliff acted upon by the sea, and the boulders of that rock on 
the slope beneath bear, he says, unequivocal signs of the action of 
currents of water. No beds decidedly calcareous were observed by - 
Mr. Clarke; but he mentions a stalactite forty feet long exhibited 
at Constantia, and the occurrence of similar stalactites on the sides 
of the mountain at Houts Bay, as indications of the existence of 
bands of limestone or calcareous sandstone. He also alludes to the 
two hills of limestone at Cape Agulhas. 
Modern Deposits.—These are confined to the dunes along the 
coast at the foot of the Blue Berg, the sand ridges on the Cape 
Flats, and the drift sand on the wide space under the slope of the 
Cape Promontory towards Constantia. Mr. Clarke also includes in 
them the concretions or calcareous sand tubes formed around the 
roots and stems of marine plants near Green Point, and at other lo- 
calities. These accumulations generally assume the form of an 
elongated tumulus, and are occasionally from 30 to 100 feet.thick. 
The author also alludes to the vegetable and other debris brought to- 
gether by the rains, and to the commencement by this means of an 
embryo lignite formation on one side of the Cape Flats. 
Springs.—The well-water in Cape Town is considered unwhole- 
some. Under Table Mountain is a spring which rises from the gra- 
nite, and is computed to throw out daily 150,000 gallons; and at 
* For an account of Dr. Smith’s discoveries at Cedar Berg see Mr. 
Murchison’s Silurian System, p. 583. 1839. 
