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NOTE
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69
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layer
by layer. While the last sheets of this book were in the press Sir J.
B. Stone, M.P., F.G.S., sent me a collection of specimens which he had
recently received from this mine, among which were pieces of the
diamond-bearing rock, of which the deepest was labelled 1,400 feet, and
I saw blocks from nearly as far down in a collection shown to me by Mr.
W. Crookes, F.E.S. A particularly well-preserved specimen which he has
lent to me for study came from 1,320 feet.
He
has also favoured me with a copy of a section representing the
workings in this De Beers mine. The shaft has reached a depth of quite
1,500 feet, and from it the lowest level is being driven. The section
of the ' country rock,' outside the ' pipe ' containing the
diamond-bearing breccia, is as follows: (1) superficial debris, (2)
basalt, (3) black shale, (4) ' melaphyre,' (5) quartzite, (6) '
slate'—probably only a hard shale, (7) quartzite and ' slate.' Dykes
(probably basaltic) pierce into (5), through (6) and (7). The '
melaphyre ' (4) is about four hundred feet thick. The area of the
workings is twenty-two acres. It is the least of the four mines
mentioned on page 1; Du Toits Pan, the largest, being forty-five acres.
Since Professor Lewis wrote, another important mine (the Wesselton) has
been opened; it is included within the same circle as the last-named.
T. G. B.
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