Revieivs — Geology of Africa. 179 



of the existence of metallic carbides in the interior of the 

 earth will explain the formation of hydrocarbons and other 

 phenomena observed in connection with volcanic eruptions. 



J. J. H. T. 



IV. — Geology of Africa. 



THE Geology of Africa in relation to its mineral wealth is the 

 title of a paper read before the Federated Institution of 

 Mining Engineers in 1896, by Mr. Walcot Gibson, F.G.S. This 

 paper, accompanied by a neat little map printed in colours, has now 

 been published. The map shows very clearly the general structure 

 of the great continent, or rather of the considerable portion of it of 

 which we have information that can be represented on a geological 

 map. There is yet a large area extending from British Bechuana- 

 land northwards through the Congo State and to the south of the 

 Libyan Desert, which for the present remains blank, but which ere 

 long will be made more accessible by the railway in course of 

 construction from Mombasa to Uganda. Koughly speaking, how- 

 ever, we still know nothing (or next to nothing) of the geology of 

 a tract almost equal in size to the whole of Europe. That the 

 Geological Eecord is well represented in Africa, is evident from the 

 full Table of sedimentary and eruptive rocks ; but as the author 

 remarks, " by far the larger portion of the continent as yet known 

 is composed of metamorphic crystalline rocks." These rocks show 

 indications of containing many valuable and precious minerals ; 

 they are not so barren as would appear at first sight, but our 

 knowledge of them is at present very scanty. The crystalline 

 schists appear to be richest in the territory of the Chartered Com- 

 pany. Newer than this metamorphic series is the famous Banket 

 formation of South Africa ; its precise age, however, has yet to be 

 determined. Nor is it possible as yet to state definitely the true 

 sequence on the Eand, for, as the author has himself shown, there 

 is much overthrusting of the strata. 



Attention is directed to the various beds of coal, to the possibility 

 of asphalt-deposits being found in East Central Africa, and to sundry 

 other matters of practical interest. The general structure of the 

 continent and the leading facts relating to its geology are clearly 

 pointed out, and the author gives a useful list of the leading works 

 on Afi'ican geology. He rightly urges that " sooner or later 

 a mineral survey of South Africa will have to be seriously under- 

 taken, in order to arrive at some approximation as to the extent 

 and distribution of the mineral-bearing districts. South Africa and 

 this country would have everything to gain by a Government 

 Geological Survey, as such a survey, being made independently of 

 any personal interest, would tend to reassure the investing public 

 and convince it that the mineral wealth of South Africa is very 

 great." 



