LTDENBTJEG AKB DE KAAP, TEANSVAAL, SOUTH AFEICA. 577 



in an inland sea, from water holding much silica and some lime in 

 solution. 



The chief exposure of these chalcedolites is along the Blyde-river 

 valle}', hest seen on its western side or escarpment, where the rock 

 occurs in two series, the lower several hundred feet in thickness, 

 with shales above, below, and between. It contains fine gold in 

 places, and, where in a decomposed state, it has been worked as so- 

 called " rotten-reef" to a considerable extent. There are numerous 

 old workings in it, following fissure-veins or old weathered crevices, 

 frequently on an extensive scale, as in Eotunda Creek, which opens 

 to the Blyde River, and again a few miles to the west of Pretoria. 



Still higher up in the shales, there are series of sandstones, some 

 compact and very highly metamorphosed, others more coarsely 

 crystalline, and resembling those of De Kaap. These and the asso- 

 ciatad conglomerates are sometimes found to be auriferous. 



These Devonian rocks moreover are traversed by dykes of diorite 

 and other trap rocks ; and immediately upon them, with an uncon- 

 formity not very strongly marked, but still probably representing an 

 extended period, rest the "High- Veldt Beds" *. 



6. Sections and Auriferous Deposits, a'-q'. — The following are 

 brief notes of sections, commencing on the south at De Kaap, and 

 ending on the north in the Orighstad Yalley : — 



a. At De Kaap " the lowest rocks of this series are highly crys- 

 talline sandstones and conglomerates .... Immediately above the 

 sandstones is a series of shales ; " these are overlain by another 

 series of sandstones on the higher ground to the west, succeeded 

 by more shales which pass in under, or are replaced by, the cherts 

 and quartzites of the Eland's-Spruit Valley. 



The conglomerates here, and in a less degree the sandstones, are 

 auriferous (see above, p. 576). The shales above the sandstones 

 enclose veins of auriferous quartz, one of which jdelded gold at the 

 rate of upwards of an ounce to the tonf. 



b'. — The Godwaan Plateau is on the upper of the two series of 

 sandstones, which are exposed to a considerable depth in many 

 natural sections, such as krantzes and caves, as well as in the 

 mines. Shales occupy the surface, sloping down towards Eland's- 

 Spruit Valley ; both these and the sandstones are crossed by quartz 

 reefs and dykes of diorite. 



There are several " reefs " on this plateau, some of them being 

 very rich in gold. (1) The " Homeward-Bound Eeef," which, so far 

 as opened, is a vein of soft saccharoid quartz, with some hard quartz, 

 much earthy matter, and oxide of iron, several feet in width, 

 striking IS", and S., and enclosed in fairly well-defined walls. The 

 lode, however, is much split up, and, as it were, spread out near the 

 surface, becoming more compact and regular below. I have no data 

 for estimating the yield of gold from this lode, which is certainly 

 rich, for some hundreds of ounces are obtained every week by small 

 machinery. The gold is remarkably fine, like flour, and requires, 



* Quart. Journ. Geol. See. vol. xl. (1884), p. 660. 

 t Eeport, Dee. 1884. 



2b2 



