26 PBOCEEDINGS OP THE GEOLOGICAX SOCIETY. [NoV. 8, 



found their way to tlie nuclei of the present period, the Vaal valley 

 and those of its tributaries, the Reit and the Hart, and the pans and 

 , sheltered spots where isolated diamantiferous farms exist. 



It is difficult to give an exact chronology of the changes ; and I 

 am still engaged in the study of that part of the subject. I am sa- 

 , tisfied, however, from what I have now advanced, that the following- 

 points may be regarded as demonstrated : — ■ 



1. The diamonds originally belonged to one of the members of an 

 ancient metamorphie series, and probably to a talcose slate. 



2. That these rocks occupied the heights during a later period of 

 trappean upheaval. 



3. That a period of lakes prevailed during and after this trappean 

 upheaval ; and that we have the last traces of these in the pans 

 of the region, many of which have become dry, filled up, and many 

 more are now extinct. 



4. The Yaal River may have possibly connected a chain of these 

 lakes. 



5. The processes of denudation have caused the ancient rocks to 

 vanish, the greenstone to reveal itself in all directions, and the 

 detritus and debris have found their way into the centres of drain- 

 age — the Vaal Kiver and its tributaries and the isolated spots and 

 pans of the Orange-Eiver Eepublic. 



6. It is undoubtedly the case that some of the diamantiferous soil 

 is recent as a deposit in its j)resent position. This is accounted for 

 by the great amount of surface-drainage and carrying in connexion 

 with Soiith-African iioods. The soil is continually being changed 

 from one place to another. A surface-flow of water, bearing mud, 

 stones, &c. along with it, accompanies every thunderstorm. The 

 soil associated with the diamond in the pans at considerable depth is 

 purely the detritus of talcose slate or clayey limestone, and cannot be 

 recent, and was probably deposited in the lake-period ; accordingly 

 the date of the first dispersion of the diamond from the original ma- 

 trix is of considerable antiquitj^ ; but during the lake-period and 

 subsequently it has been going on. 



7. It woiild be very foolhardy in any one to say that no great 

 amount of the diamantiferous soil has been carried down by the Vaal 

 to the Orange Eiver. Possibly the absence of minute diamonds along 

 the Vaal diamond-field is to be explained by the river having carried 

 them downwards. There is, however, every reason to believe that 

 the same diamantiferous soil occurs along the Orange Eiver. Dia- 

 monds have been found on both sides of that river. We know less, 

 meanwhile, of the course of tlie Orange Eiver and the territory di- 

 rectly to the north and south of it than we do of the interior of 

 Africa. 



DlSCTTSSION. 



Mr. Woodward mentioned that Mr. Griesbach and M. Hiibner 

 had been over the country described in these papers, and had com- 

 municated a map of it to Petermann s Journal. 



Mr. Griesbach stated that the rock described as metamorphie in 



