198 TRANSACTIONS. 
found in considerable quantities in a coarse conglomerate on the 
banks of the Vaal River. The stones in this conglomerate are all 
water-worn and about the size of a hen’s egg. They appear to 
begin suddenly at Warrenton and Sixteen streams, and are found 
along its course for a considerable distance. Probably the river 
has cut into some mine similar to those at Kimberley, and the 
diamonds have been washed out of it. It is worth noting that at 
Warrenton this conglomerate is 60 or even 100 feet above the pre- 
sent bed of the river. 
A very remarkable point about the occurrence of these mines 
consists in their being distributed along a narrow belt of country. 
This runs N.N.E. by 8.8.W., and is about 80 miles long and 2 or 
3 miles broad. Such a distribution may perhaps point to a line 
of weakness, along which voleanic craters were formed. It is now 
generally admitted that the diamond mines are simply volcanic 
necks or pipes, and they appear to occur, so far as I could judge, 
about the epoch of the Kimberley shales. 
The following sections shew the rocks encountered in the 
shafts where records were kept : 
Kimberley Central. De Beer’s, No. 1. De Beer’s No. 2. 
DEbris’- “=: ... A few feet. A few feet. — 
Red Sand on 3 55 Das, 3 feet. 
Dolerite ... S20), ADDO! s5 BS 29; 5 gles 
Black and other 
Shales ... 240-250 ,, 195. -.; p75 
Amygdaloidal ... 626 ,, ? Bee 
Ancient ... ...Diabase of Dunn. ? Not bottomed. 
The sections of De Beer’s are peculiarly interesting, as they 
shew that the dolerite thins out as one proceeds away from the 
mine. This is also shewn, though not so well, at the Central 
Mine, as the bed of delerite there is 6 feet thicker as exposed at 
the edge of the mine than it is where encountered by the shaft at 
some little distance from the edge. This thinning out of the 
dolerite, and especially its upward course from the mine, as well 
as the tact that it did not extend over the blue ground, tend to 
prove that it proceeded from the openings now filled by diamondi- 
ferous earth. The black shale below is also hardened (as one 
would expect), though I could not see the junction to tell if there 
was a special hardening there. I may mention here that the edges 
of the black shale are in the Central and Du Toit’s Pan inclined 
upwards at an angle of some 45°. This is clearly shewn also at 
EE! 
