676 "W. H. PEKNOfG Oir THE GOLDPZELDS OF 



granitic range ' running in a N.E. direction from lat. 20° 30' to 



» " 



5. Devonian ? Rocks. — After the rocks wMcli I have referred to 

 as Silurian had been tilted into their present vertical position by 

 the upheaval of the central mass of granite of the Kaap Yalley, 

 they V5^ere cut down to a " plain of (probably) marine denudation." 

 This old plain is at an elevation of 1700 or 1800 feet above the 

 present general level of the Kaap YalLey, which has, of course, been 

 much more recently excavated. Upon the upturned and denuded 

 edges of the Silurian rocks, those which I here provisionally term 

 " Devonian " were deposited. (The '^ Megaliesberg Beds " of my 

 paper on the Coalfield, Q. J. Gr. S. vol. xl. p. 660.) 



At the base of these Devonian rocks is frequently seen a series of 

 conglomerates and sandstones (with some shales), which is fairly 

 well exposed about De Kaap, " formed from the waste of the under- 

 lying Silurian beds, and of any quartz veins that they may have 

 enclosed " t. The Kaap sandstones are highly crystalline, some 

 coarse, others fine in texture, in thick beds which have weathered 

 into massive tabular blocks, which impress a peculiar distinctive cha- 

 racter upon the appearance of the country. 



These sandstones and conglomerates thin out to the north, as the 

 immense series of shales (with occasional sandstones), by which they 

 are overlain, rests directly upon the granite on the other side of the 

 Krokodil River. At De Kaap they afiPord additional evidence that 

 rich gold-lodes exist below them, or at no great distance, in the 

 Silurian rocks from which they were derived ; for they are frequently 

 auriferous, containing not only fine gold but nuggets, especially the 

 conglomerates. An analogous case, but of course one of recent 

 date, is the occurrence of fine gold in the sand of the sea-shore (and 

 probably, of course, gold in the gravels) upon the west coast of N'ew 

 Zealand. 



Above the sandstones comes a very large series of shales and flag- 

 stones, fissile and thin-bedded, which generally are grey, but weather 

 to yellow or dirty yellow or dirty brown. In some localities, as 

 along the valley of the Eland's Spruit, there occurs a series of cherts 

 and quartzites, which appear to replace the lower shales. 



High up in the shales, but not by any means near the top of them, 

 are two or more series of a peculiar, blue, fine-grained, calcareo- 

 siliceous rock, to which Mr. A. C. CruttweU and myself have given 

 the name of '•' chalcedolite." "We adopted this term in consequence 

 of the chalcedonic texture frequently displayed — indeed, some por- 

 tions of the rock are true chalcedony. Sometimes it occurs in 

 amorphous masses, weathered to a grey colour, and to a peculiar, 

 rough, trachyte-like surface ; but mostly in thin beds, 2 or 3 inches 

 in thickness, with earthy partings, the lines of lamination being 

 wavy and indistinct, except where exposed by weathering. The 

 rock appears to be the result of intermittent deposition, probably j 



* Guide to the Goldfields, p. 62. 

 t Eeport, Dec. 1884. 



