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378 THE DIAMOND
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Two
of kimberlite from Africa by Prof. H. Carvill Lewis of which I was the
least decomposed rock with few shale enclosures and II, the more
decomposed rock with many shale enclosures (diamondiferous), are as
follows:
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There
are no horizontal layers in the kimberlite nor are there any beds of
foreign rock in it, the floating reef being distributed throughout very
irregularly, but there are very small vertical crevices in the
kimberlite, filled with a foreign mineral resembling talc, which divide
the kimberlite into vertical columns. These columns differ slightly
from each other in color, composition and contained minerals, though
each is the same in character throughout, and all are in general alike.
The most important difference is that some of these columns are much
richer in diamonds than others. The western end of both the Kimberley
and De Beers mines were very poor, the richest part of the latter
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