1 66 Cape of Good Hope. paetl 



sea, wherever the vessel anchored, was ascertained by 

 croAv-bars being let down, to consist of white calcareous 

 matter. Hence it seems that along this coast, as at 

 Bermuda and at Keeling Atoll, submarine and sub- 

 aerial deposits are contemporaneously in process of 

 formation, from the disintegration of marine organic 

 bodies. The extent of these deposits, considering their 

 origin, is very striking ; and they can be compared in 

 this respect only with the great coral-reefs of the Indian 

 and Pacific Oceans. In other parts of the world, 

 for instance in South America, there are superficial 

 calcareous deposits of great extent, in which not a trace 

 of organic structure is discoverable ; these observations 

 would lead to the enquiry, whether such deposits may 

 not, also, have been formed from disintegrated shells 

 and corals. 



Cape of Good Hope. 



After the accounts given by Barrow, Carmichael, 

 Basil Hall, and W. B. Clarke of the geology of this 

 district, I shall confine myself to a few observations on 

 the junction of the three principal formations. The 

 fundamental rock is granite, 1 overlaid by clay-slate : 

 the latter is generally hard, and glossy from containing 

 minute scales of mica ;. it alternates with, and passes 

 into, beds of slightly crystalline, feldspathic, slaty rock. 

 This clay-slate is remarkable from being in some places 

 (as on the Lion's Rump) decomposed, even to the depth 

 of twenty feet, into a pale-coloured, sandstone-like rock, 

 which has been mistaken, I believe, by some observers, 



1 In several places I observed in the granite, small dark-coloured 

 balls, composed of minute scales of black mica in a tough basis. In 

 another place, I found crystals of black schorl radiating from a 

 common centre. Dr. Andrew Smith found, in the interior parts of 

 the country, some beautiful specimens of granite, •with silvery mica 

 radiating or rather branching, like moss, from central points. At 

 the Geological Society, there are specimens of granite with crystallised 

 feldspar branching and rad ating in like manner. 



