Mr. Bain on the Geology of Southern Africa. 191 



coast. In some places it attains a thickness of upwards of 100 feet, and contains 

 imbedded shells of the common land-snail in great abundance, as well as various 

 recent animal and vegetable remains*. At Cape Agulhas the new lighthouse has 

 been built of this rock, but it is generally used merely for lime-burning. 



Thin beds of calcareous tufa are also found overlying the ReptiUferous strata in 

 all parts of the interior, and are invariably used by the inhabitants for lime, there 

 being no regular stratified limestones in South Africa. 



The Cango Cavernsf in the Division of George are famous for their large and 

 beautiful stalactites and stalagmites, which afford a very pure carbonate of lime, 

 much superior to the tufas. Smaller caves of the same are found in different 

 parts of the colony. 



Frequently, resting on the above or on the older rocks below, are found beds of 

 recent marine shells exactly the same as those at present inhabiting the Indian and 

 Atlantic Oceans, — some specimens accompany my collection of 1847. I have found 

 them near the mouth of the Great Fish River, Kowie, Port Elizabeth, Van 

 Staaden's River, Mossel Bay, and Lion's Head, Cape Town (see Section, No. 4) . 

 and they are also to be seen all along our western coast. In some parts they 

 occur in beds of considerable thickness, imbedded in loose sand mixed up with 

 bones of recent land-animals, and even many specimens of native pottery and 

 other works of man ; so that this raised beach, for such it must be, has been 

 uplifted to its present height during the historical period. Its height varies from 

 20 to 300 feet above the sea-level j. 



A superficial ferruginous deposit, which is found in the greatest abundance on 

 the Cape Flats, and there covering the clayslate, consists of an oxide of iron, 

 derived either from the clayslates themselves or from the neighbouring sandstone 

 mountains^. In some places it reaches the thickness of 10 feet, and is much used 

 for road-purposes. This ironstone is found in small patches on many of the 

 marine formations throughout the colony. At Kalga Springs, near Port Elizabeth, 

 it is curious to observe the ferruginous deposits forming and indurating, as it were, 

 before our eyes, as the water charged with the iron flows away from the source ; 

 this is illustrated by some specimens in my collection of 1847. 



Hot, tepid, and cold chalybeate springs are found in various parts of the colony, 

 and are much resorted to by the inhabitants as a cure for all diseases. None of 



* See also Capt. Nelson's observations on the " ^olian " beds at Algoa Bay, Quart. Journ. Geol. Soc. 

 vol. ix. p. 206, note. — Ed. 



t For a detailed description and illustration of these Caverns see G. Thompson's 'Travels in Southern 

 Africa,' vol. i. p. 275, &c. 1827, 8vo. 2 vols.— Ed. 



I See also the Rev. Mr. Clarke's Observations, Proc. Geol. Soc. vol. iii. p. 420. — En. 



§ See also Mr. Darwin's Observations, ' Volcanic Islands,' p. 143. — Ed. 

 VOL. VII. SECOND SERIES. 2 D 



