198 Becker — Auriferous Conglomerate of the Transvaal. 



the sand grains have been largely attacked by sericite and that 

 a portion of the irregularity of outline is due to this cause. 

 The matrix also contains prisms, often grouped in fan-shaped 

 aggregates, of a colorless secondary mineral, possibly an amphi- 

 bole. The same or a similar mineral was noted by Koch and 

 by Pelikan. Its determination is not essential for the purposes 

 of this paper. 



It is worth while to observe that the cement of the conglom- 

 erate is distinguishable from ordinary vein quartz as seen under 

 the microscope. The crystallization of the cement has been 

 accompanied by corrosion of arenaceous minerals, and the 

 matrix is mingled with the products of this action as vein 

 quartz seldom or never is. On the other hand, the cementing 

 material of the conglomerate and that of the quartzite at a 

 distance from the banket reefs appears to be indistinguishable 

 under the microscope. In other words, the banket is a coarse 

 heterogeneous quartzite. 



It is well recognized on the Hand that, other things being 

 equal, the coarser pebble carries the greatest quantity of gold. 

 Usually the rich ore is heavily sulphureted, but this is not 

 invariable. As a rule, the thinner portions of reefs are richer 

 than thicker portions. It is usually the under portion of a 

 coarse streak which is richest, but such a coarse streak is some- 

 times met with in the lower portion of a reef and sometimes 

 in the upper portion. There is in this respect no general rule. 

 It is said that the sandstone near the banket in rare instances 

 carries gold. It is known, however, that in some alleged 

 instances of this kind the gold was really confined to the parting 

 between the sandstone and the banket. The banket is patchy. 

 There are rich patches and poor ones, rich patches in poor 

 ones, and poor patches in rich ones. Sometimes these patches 

 have an elongated form, and then are often called " chutes." 

 Opinions differ among managers as to whether there are on the 

 Rand any real continuous chutes or channels, such as are almost 

 invariably found in gold-bearing quartz veins. I could learn 

 of no case which was an indubitable chute as distinguished 

 from an elongated patch. Much less does any rule hold, as 

 in most gold quartz districts, concerning the pitch of ore 

 bodies on the surface of deposition. For the most part the 

 bodies are certainly patches, and, if there are true chutes 

 as well, two distinct types of deposit are present. The general 

 uniformity of appearance and conditions militate against this 

 view. 



It has already been mentioned that the Lower Cape is inter- 

 sected by numerous dikes, mostly of diabase or closely allied 

 rocks, these dikes being connected in the most evident and 



