14 PROCEEDINGS OF THE GEOLOGICAL SOCIETY, [NoV. 8, 



junction of the two rivers, a distance of upwards of 100 miles 

 below Pniel. 



The agencies that have worked out the one basin have without 

 doubt operated in the formation of the other, both being valleys of 

 denudation ; and the whole of such deposits as those found upon 

 the lower plains, and along the banks of the rivers, must have ori- 

 ginated within the boundarj-line that has here been pointed out as 

 the great watershed of the rivers running into the Atlantic and the 

 Indian Ocean. It is therefore within this limit that we must 

 seek for the origin of the diamantiferous gravels and ether deposits 

 of the Yaal. 



Rocks and Fossils of the Upper Drainage-area. — Before proceeding, 

 however, it will be well to consider the indications we possess of 

 the character of some of the formations that form different portions 

 of this outer boundary -line. The evidence in my possession is scanty, 

 but of great interest. Commencing on the northern boundary, we 

 find that in the Magalies Berg and Pretoria there are micaceous 

 rocks, vastly different from those belonging to the great Dicynodon- 

 formation of the Colony, consisting of and containing large quan- 

 tities of mica, with ores of cojDper and lead, the latter, it is said, very 

 abundant. See ISTos. 19, 20, 21 in the Appendix. 



From this spot to the sources of the Umzimvoobo, on the southern 

 side of the Quathlamba, I have been unable to obtain rbck-speei- 

 mens ; but from this last locality I was fortunate enough to secure 

 several, collected by Mr. Whitmore from the gravels along the 

 watercourses. See No. 22 in Appendix. 



These form a most interesting collection, and might be easily 

 mistaken, both from their shape and character, for some of the 

 pebbles obtained from the diamond-bearing gravels of the Vaal. 



From the Zeitza, a small stream rising in the same mountains, 

 similar specimens were obtained (Nos. 23 & 24 in Appendix). 



Also from the heads of the T'somo, a river rising among the 

 branches of the mountains that form the junction of the Quathlamba 

 and Stormberg ranges, rocks very similar to some of the fragments 

 found in the valley of the Yaal. See Nos. 25, 2Q, and 27 in the 

 Appendix, 



Origin of the Gravels. — The conclusion to be drawn from the con- 

 sideration of these facts taken collectively (the whole of these speci- 

 mens being procured from the southern side of the mountains, from 

 the northern side of which both the Orange and Yaal take their 

 rise) is, I think, that zones of fossil wood are found stretching along 

 these mountains, and that they contain rocks which are similar to 

 many of those found in the Yaal-River gravels. It is therefore 

 highly probable that the fragments of the fossils found in them, 

 and of the various, yet very similar, rocks, have both come from 

 the same source, namely the elevated ridge that forms the water- 

 shed of the rivers that flow into the two different oceans, and that 

 during the vast denudation to which the strata have been subjected 

 large portions have been carried away in the one or the other direc- 

 tion. On the north they have been promiscuously intermingled 



