1871.] SHAW DIAMOND-rrELDS OF SOUTH AFRICA. 21 



Pebble of peculiar Agate-breccia, with ancient fracture. 



Subangular Agate, various ; and fresh fragments of Agate. 



Subangular piece of Magnetite. 

 No. 26. From the T'somo, M. 2. Page 14. 



Coarse grey Quartz-grit, weathering brownish, with dissemi- 

 nated Mundic (small cubes). Hard coarse Clay-schist, with 

 disseminated Mundic. Small fi-agment of calcareous vein- 

 stone with Copper-pyrites ; small fragment of quartz-vein 

 with Copper-pyrites ; a morsel of quartz-vein with Iron- 

 pyrites ; and a small piece of tine-grained Galena. 

 No. 27. From the T'somo, M. 1. Page 14. 



Haematite with quartz. 



EXPLANATION OP PLATE I. 

 Map of the Vaal Eiver from Plaat Lerg to the Ecit Eiver. 



3. On the Geology of the Diamond-Fields of South Africa, By 

 Dr. JoiiiS^ Shaw, Colcsberg, Cape Colony. 



(Comimmicatecl by Dr. Hooker, O.B., F.E.S., F.G.S.) 



[Abridged.] 



We have presented in the various parts worked for diamonds up to 

 the present date two apparently different classes of soil in which 

 diamonds are found imbedded. The one class exists along the Vaal 

 Biver and its tributaries, the Peit and Hart Ravers ; and the other 

 occurs in the Orange-lliver Pepublic, in isolated spots, generally cir- 

 cumscribed, and in many cases in what are called " Pans," which are 

 basin-like hollows, in wet seasons more or less filled with water of a 

 saline character, in dry seasons presenting a whitish surface satu- 

 rated with salts. 



I shall endeavour to show that there is really no distinction in the 

 geological origin of the two classes. It will be convenient, however, 

 in the first place to treat them separately, for the sake of clearness. 



The prevailing rocks of the Yaal region and the isolated diamond- 

 farms are trappean — greenstone and basalt. There is every indi- 

 cation that the upheaval of these has been continued throughout a 

 vast length of time, and has extended until recently, geologically 

 speaking. The summits of the hills consist of trap, which has been 

 protruded through vast layers of sedimentary strata — generally 

 calcareous sandstones, clay-slate, and such like rocks, all remarkably 

 barren of fossils. Yery httle disturbance is shown in the lie of these 

 sedimentary rocks. Hence the prevailing character of the ranges is 

 tabular, though dome-like, conical, and even pointed peaks are 

 seen. They are dispersed more or less circularly around dreary 

 flats, which are in many instances of considerable extent. The trap, 



