1871.] SHAW DIAMOND-FIELDS OF SOTJXn AFEICA. 25 



cesses have in time, no doubt, aided in enlarging it ; and its waters, 

 having been confined and imprisoned, have become salt, from being 

 at first after the upheaval brackish. This, I feel convinced, is its 

 history in a few words. 



But, in addition, gradual wearing of the tilted strata would give a 

 base-soil of the constituents of the rocks, which are mainly siliceous 

 and calcareous ; hence the calcareous tufa and calcareous soils so 

 abundant everywhere, and conspicuously so in the pans. The hard- 

 ness of this substance merits for it the name of rock ; but it is depo- 

 sited in the same way as an ordinary earth. It is afterwards kept 

 compact by its avidity for moisture, which it receives from the occa- 

 sional rains. When broken up and dried by exposure, it becomes 

 quite friable, and moulders into loose powdery masses. 



The Icalh (as the calcareous tufa is popularly called) of Du Toit's 

 Pan does not, however, appear to be very siliceous, and, on^this ac- 

 count, is not so consolidated and hardened as in many other parts of 

 the country, especially along the Lower Vaal, where the silex of the 

 amygdaloid is chemically combined with the calcareous sediment from 

 the same and other rocks. 



The question of Diamantiferous indications is one of some impor- 

 tance. Prom the beginning of the digging, garnet and tourma- 

 line have been regarded as associates of the diamond. These prevail 

 along the Yaal and in the isolated fields in all good diamantiferous 

 soil. In Du Toit's Pan a peculiar substance is favoured by the diggers, 

 consisting of a fine clayey detritus, glistening with talc, and abounding 

 in garnets, tourmaline, and corundum. It is of a greenish colour, but 

 presents occasionally the appearance of burnt brick: when impregnated 

 with iron. It is called, from its resemblance to bran, " semmels." 

 This I have considered the correlative of itacolumite — a substance I 

 have failed to discover in any of the " rushes." 



These diamantiferous indications apply throughout the whole of 

 the diamond-producing region. Even the talcose detritus of Du 

 Toit's Pan occurs with varying characters in occasional patches of 

 the Yaal-Eiver diggings. At Pniel, where mining to some depth 

 was carried on, it occurs close to the fundamental rock — greenstone. 

 I am therefore disposed to think that the talcose slate, which pro- 

 duced the detritus, was the original matrix of the diamond, and that 

 this rock was one of the series of metamorphic rocks — gneiss, mica- 

 schist, &c. In the diamantiferous pans traces of thesehave been 

 preserved, chiefly from their isolation and from being undisturbed, 

 as the tract along the Yaal Eiver has been. But the inference is 

 that the original diamantiferous rock has extended throughout the 

 whole region of that part of South Africa. This and the associated 

 rocks were disturbed by the greenstone upheavals. It is likely that 

 these upheavals occurred at various times. During and subsequent 

 to these disturbances was the great lake-period of South Africa, when 

 the immense deposits of lacustrine formations were made. The 

 ancient rocks yielded to denudation and wearing, in some cases went 

 towards the formation of trap-conglomerates, and generally have 



