56 Prof. T. Rupert Jones — Diamond Fields of S. Africa. 



rites, perfect. Specular Iron-ore, Pea-iron-ore, and other Oxides of 

 iron. Ilmenite, waterworn fragments. 



Professor Tennant ^ has also received a large piece of greenstone- 

 amygdaloid, having its cavities mostly filled with Calcite, a few 

 with Chalcedony, and still fewer with Greenearth and Olivine. 



If not denuded everywhere down to the underlying palaeozoic 

 rocks, possibly the Karoo basement-bed of "trap-breccia" or 

 boulder-deposit (if it ever reached thus far)^ may have been left 

 exposed somewhere along this great valley, and yielded its granitic, 

 trappean, and other blocks, which elsewhere along the outcrop of 

 this remarkable band, in Natal and across the Cape Colony, are often 

 of massive proportions. 



Not only this great breccia, but other strata of the Karoo series 

 contain granitic material f and some of even the highest of them are 

 composed of it, some of the sandstones being quartzose with a little 

 mica, and much decomposed felspar. Hence any simple minerals 

 once in the granite or old schists may have been liberated, unaltered 

 and unworn, on the further and perhaps recent degradation of old 

 granitic debris. A perfect and delicately thin crystal of tourmaline, 

 from the Vaal, now in Dr. Atherstone's possession, indicates this, as 

 well as numerous perfect crystals of quartz, hepatic pyrites, etc. 

 Many of the minerals in the gravel seem to be traceable to igneous 

 (amygdaloid) rocks, and some to palaeozoic rocks, in place not far 

 off.* Mr. Bain long ago observed ^ that the Orange Eiver, to the 

 west of Aliwal, has "pebbles of serpentine, steatite, asbestos, agate, 

 and amygdaloid, both of black and white colour; these minerals being 

 entirely diiferent from those which form the materials of the pebbles 

 occurring in the river-beds within the Colony." Certainly for such soft 

 minerals and rocks as some of those here mentioned, and for pieces 

 of asbestos (tremolite) veins picked up on the Vaal (Grey), there 

 must be such neighbouring sources as outcropping masses of meta- 

 morphic rocks would afford, like the " Asbestos Mountains " lower 

 down the Orange Eiver. Asbestos, serpentine, and steatite are 

 elsewhere associated with metamorphic rocks, as they are on the 

 Orange Eiver and the Upper Vaal. The quartz and amethyst 

 crystals might be derived either from amygdaloidal geodes (Gregory), 



' See also Prof. Tennant's lecture on South- African Diamonds, Journal Soc. Arts, 

 Nov. 25, 1870, p. 15, etc. Eeported in the Geol. Mag. for January last, p. 35. 



^ The palseozoic rocks of the Transvaal having been at least a shoal, overlapped, if 

 not wholly covered, by the Karoo formation, it is highly probable that the latter 

 commenced with the boulder-bed here as elsewhere. It is possible, however, 

 that the latest beds only of the Karoo formation reached thus far ; and hence the 

 enigma of Palaeozoic coal-plants in the same section with the Mesozoic fossils in the 

 Stormberg. 



3 See also Dr. Sutherland's observations on the blocks of porphyritic granite in the 

 arkose, or granitic sand, of the Karoo beds in Natal, as well as in the breccia (which 

 in 1855 he thought to be of volcanic origin). Quart. Journ. Geol. Soc, vol. xii., 

 pp. 466 and 467. 



* There is selenite (small sagittate macles ; Grey) of local origin, which may have 

 resulted from decomposition of pyiites in the drift, and reactions with the tufa. 



^ Trans. Geol. Soc, 2nd ser., vol. vii., p. 58, 1845. 



