592 REPORT— 1889. 



tion of Siberia, lias a general slope which is southwards, causing its great rivers, 

 the Ural, Volga, Don, &c., to flow southwards still ; thus affording a sample by 

 which to test the former condition of the great region stretching from the Carpa- 

 thians and the Baltic to Behving Straits. 



The effects of this change of physical feature must obviously have been manifold. 

 The existence of a great Central Asiatic sea would greatly temper the Siberian 

 climate, while the southern flow of its rivers would affect the distribution of 

 animal and vegetable life, and offers at least a reasonable solution of the difficulties 

 surrounding the migration of birds in the Palse-arctic region, while it sweeps away 

 the hypothesis that the mammoth remains of Siberia are the wreckage of river 

 portage. 



8. On the Witwatersrand Goldfields. 

 By Edward Bates Dorset, Mem.Am.Soc.O.E., Mem. Am .Inst.M.E . 



In the early part of this year the author visited South Africa on business con- 

 nected with railways and mining, which made it necessary for liim to examine 

 •critically into the mining capabilities of the southern portion of the Transvaal, 

 which section is called promiscuously the Rand, Witwatersrand, or the Johannes- 

 burg district. The mines there are more developed than those in any other part of 

 the State. The following is a brief description of the principal features of this 

 •district. As yet there has been no scientific or systematic study of the geology of 

 this district ; all that is known of it has been discovered or developed by the 

 workings of the mines or in the search after gold-bearing veins. 



The geological formation consists of a series of strata of sandstone, quartzite, 

 elate, and conglomerate, all evidently deposited quietly by water. Part of the 

 northern and eastern edge of this basin has been tilted up to an angle of 25 to 45 

 degrees from the horizontal by the irruption of diorite, and it is probable that the 

 remaining portions of the vein will be found also tilted up, forming a basin over 

 100 miles long east and west, and 40 miles wide north and south. The dip on the 

 northern edge is to the south, and on the eastern edge to the west. Johannesburg 

 is on the extreme northern edge of this basin. 



The formation is similar to that of coal, and will no doubt be found as regular 

 as that of most coal basins. 



An inferior quality of coal is found in workable quantities within 200 yards of 

 workings on the Main Reef which produce good gold ore ; and it is very likely that 

 ore containing gold, and coal for fuel to crush it, will yet come from the same shaft. 



As yet no fossils have been discovered from which the geological age of this 

 formation can be ascertained. 



The gold is contained in the conglomerate strata in quantities which vary 

 from a trace to 8 ounces per ton. There have been a large number of these 

 strata discovered, and probably many more will be found as work progresses. These 

 strata vary in width from a few indies to many feet, but each one when compared 

 to itself is very uniform in its yield of gold and in thickness. 



In some few places the formation has been broken by the irruption of diorite, 

 but not to the extent that could be expected when the size of the basin is con- 

 sidered. 



These conglomerate veins are called locally ' banket reefs ' ; in this paper they 

 will be called ' veins,' being merely interstratified beds or veins. They are composed 

 mostly of quartz, quartzite, and sandstone pebbles, varying in size from an inch in 

 diameter down, though sometimes larger, the cementing matrix being composed of 

 oxide of iron, sand, and some clay. This cement is generally soft, but in some 

 cases it is so liard that when the ore is broken the quartz pebbles will break before 

 the cementing matrix. As a rule the pebbles contain no gold. The gold is fine, 

 with sharp angles, not at all waterworn, and showing no signs of being alluvial. 



The Main Reef veins are among the lowest or deepest veins, and the Black 

 Reef and Zuur-Bult Reef are the top or uppermost veins of this basin. As the Black 

 Reef is very flat, with its north and south outcrop well defined, the Main Reef in 

 depth will probably follow the same course, as all were undoubtedly deposited in 



