200 TRANSACTIONS. 
from 80 to 170 miles from the sea. We have no reason to suppose 
that the deep and narrow gorges through which the Orange River 
now makes its way out of these mountains to the west always 
existed ; but we have every reason to think that these mountains 
were at one time much higher than they now are. If, in fact, one 
tries to realise this semicircular rim of mountains with the whole 
drainage of the Orange River enclosed as a gigantic lake within it, 
one will, I think, be able to explain the deposition of the Kim- 
berley shales, Caroo and Stormberg Beds, which have a so remark- 
ably regular and uniform appearance. The strata are perfectly 
horizontal now through most of their course, and the Caroo Beds, 
as well as at anyrate the coal beds of the Stormberg, are fresh- 
water deposits. 
It follows from this that Kimberley must have been during 
part of this period at the bottom of a vast inland lake, and if I 
am right in placing the formation of the craters as closely succeed- 
ing, if not during the deposition of, the Kimberley shales, the 
volcanoes must have been subaqueous. The craters would there- 
fore, after the lava had been ejected, become gradually filled up by 
mud (possibly tufactous) containing organic remains. There is 
no reason, however, to suppose that volcanic action ceased alto- 
gether. It is possible that volcanic gases or steam continued to 
pass up through this porous mass of finely divided sediment. 
Perhaps the peculiar veins found in the diamondiferous blue 
earth show that this really was the case. In St. Augustine’s mines, 
as already stated, there is a band of hardened blue running round 
the edge of the mine. In De Beer’s there is what is called “ the 
Snake,” which runs right across the mine from §.E.-N.W., and of 
a peculiar structure. In Du Toit’s Pan there is an isolated lamin- 
ated mass of rock of a peculiar kind (called Mount Ararat) in the 
centre of the blue earth, with three veins of hardened blue earth 
running across the mine from it to the sides. In the central mine 
there is a vertical narrow fissure, filled apparently by very hard 
blue earth, which appears to traverse the surrounding rocks in the 
direction of De Beer’s mine. 
I have not yet received a description of the petrological char- 
acter of these veins, and therefore cannot say more than that it 
seems to be probable that they are due to the action of volcanic 
gases at a great heat and pressure penetrating the porous blue 
earth along certain lines or crevices. Moreover, such an action of 
volcanic gases would perhaps explain the formation of diamonds 
> 
