534- Geological Society -.—The Rev. W. B. Clarke 



On the opposite side of False Bay and the Cape Flats granite 

 again rises into lofty mural precipices, capped, as on the west side, by 

 sandstone. It therefore constitutes the fundamental rock of the 

 whole of the district south of the Lion's Head, and is everywhere, 

 except at the flats between Table and False Bays, crested by hori- 

 zontal beds of sandstone. The soil of the vineyards of Cape Town 

 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- 

 tain, 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. 



* For an account of Dr. Smith's discoveries at Cedar Berg see Mr, 

 Murchison's Silurian System, p. 583. 1839. 



