180 TG BONNEY: [SEPTEMBER 
the bastite group, and I have no doubt it is the one present in the 
boulders just mentioned. The specimen accordingly represents a very 
coarse garnet-bearing bastitite.’ 
One more boulder still remains, though it requires only a passing 
notice. It is a compact greenish rock with spots of a light-coloured 
mineral. This proves on examination to be a rather felspathie diabase, 
with amyedales consisting chiefly of calcite, with chlorite, and a few 
small groups of zeolite. 
These diamantiferous plots in West Griqualand, though on a 
smaller scale than at the older mines near Kimberley, occur in a 
similar way, and are formed of a rock practically identical. Those 
now being worked are three in number, two at least of them being 
connected by a line of fissure. The rock has now been proved, and 
galleries have been driven to a depth of over 300 feet, and the 
boulders above mentioned were found at various levels down to this 
from nearly 100 feet. A section obtained just south of the middle 
“pipe” is interesting. Here a gallery was driven between two walls of 
diabase (? dykes) about four yards apart, and in the interval were four 
ribs of blue ground, parted by country rock, which is a grey mudstone, 
sometimes pebbly. The total amount of the two was nearly the same, 
but the thinnest rib of “blue” (very decomposed) was about an inch 
in width, while the thickest was rather under four feet. It is strange 
that the characteristic “ breccia” (though rather a finer variety than 
usual) should have penetrated into so narrow a fissure.” The principal 
areas, however, appear to be “blow-holes,” formed in the same way as 
parasitic cones along a crack on the flank of a volcano. 
Thus the diamond has been found to be a constituent of an 
eclogite, and the parent rock occurs as boulders in the ordinary 
diamantiferous material (blue ground). JI have no hesitation in 
claiming this coarsely holocrystalline eclogite as an igneous rock, 
though I am aware that some uncertainty has been expressed on this 
point ; but, as it happens, I have had several opportunities of studying 
eclogites, not only under the microscope, but also in the field, and am 
convinced that they are as truly igneous rocks as granites, syenites, or 
diorites. They are, indeed, rather closely allied with the last named, 
perhaps also with certain dolerites. The relationship may be expressed 
by the homely direction: “ Put some salt into the magma of an ordinary 
eclogite and it will crystallise as one of the less acid diorites.” 
The diamond then is shown to be an accidental constituent of the 
1 Pyroxenites (diallagite, bastitite, etc.) not unfrequently run very coarse, but (so far 
as I happen to have seen) in rather thin dykes or veins. See Quart. Jour. Geol. Soc. vol. 
lv. (1899), p. 290. 
2 It will be remembered that the Kimberlite of Elliot County, Kentucky, appears to 
occupy a branching fissure (Lewis, ‘‘ Genesis and Matrix of the Diamond,” p. 64). As 
this section was obtained in a gallery at a depth of 300 feet it may possibly be misleading, 
and some of the blocks of mudstone may not be im situ, but only great fragments which 
have fallen into the fissure, 
