372 E. H. L. Sc/m-arz—Gold in Cape Colo)i>/. 



constant, tending to pinch out and run into stringers, while the 

 veinstone is often cased in a layer of silvery grey-green phyllite, 

 which I take to be material that has been carried mechanically into 

 the fissure before the quartz began to form from solution. The lie 

 of the veins here also is along the strike of the rocks, and the dip 

 generally is greater than the dip of the beds, but there is a good deal 

 of variation in regard to the latter point. 



The difference between the two modes of occurrence can be traced 

 to the varying tensile strengths of the sandstones which go to form 

 the Table Mountain Series ; all grades of grain from gravel to the 

 finest meal-sand occur in the beds, and in addition the coherence of 

 the particles, due to cementing substances such as iron sulphides 

 and silica, must be very different in the successive layers. In the 

 Bokkeveld Beds, however, there is far more homogeneity in the 

 texture of the beds, although when subjected to surface weathering 

 there appears to be a good deal of variety ; in tlie bulk, however, we 

 can take the Bokkeveld Series to be made up of a continuous deposit 

 of clay-slates, with occasionally a sandy or calcareous bed. North, 

 of the mountains great banks of quartzite appear, but to the south 

 these have not been noticed, and it has been supposed that the beds 

 along the coast represent sediments which have been laid down in 

 deeper water than those to the north of the mountains. 



The ore-deposits in the quartz-veins in the Table Mountain 

 Sandstone area consist of gold, pyrites, galena, blende, and some- 

 times carbonate of iron. In the Bokkeveld area there are copper 

 and iron pyrites. All these ores I take to have been deposited in 

 the quartz-veins by lateral secretion, and not by the ascension of 

 mineral solutions from great depths. By lateral secretion I do not 

 mean to imply that the immediate walls of the veins have supplied 

 the material, as argued by Sandberger, but that the rocks within 

 a reasonable distance of the veins have done so, according to the 

 broader views enunciated by Le Conte. At the same time I believe 

 that there is an ascension of metallic substances in solution from the 

 depths, only that here this explanation of the mineralization of the 

 veins is out of the question, because the pre-Cape rocks underlying 

 the Table Mountain Sandstone and in the immediate neighbourhood 

 show no signs of quartz-veins bearing deposits of ore. 



The vertical extent of the reefs is a question of great moment to 

 the mining engineer, as upon the continuance of the reef depends 

 the successful employment of capital. If the fissures are caused by 

 an immense arm of granite, and not by a boss, then they will not go 

 down into the earth to indefinite depths. We have reefs cropping 

 out at 2,600 feet above sea-level in the Table Mountain Sandstone, 

 and in the Bokkeveld Beds they are found at only a couple of 

 hundred feet above sea-level. I consider it a low estimate if we 

 take it that at least half of the distance of the mountains from sea- 

 level upwards has been denuded away, and that the reefs originally 

 extended to 5,000 feet above the present ocean surface. The reefs 

 go at least 1,000 feet below the sea-level, for on the sides of the 

 Little Homtini River we have a section showing a reef commencing 



