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ORIGIN OF THE DIAMOND 379
being in the center. Fifteen of these kimberlite columns have been observed in the Kimberley mine.
From
the nature of the kimberlite, and the condition of the reef
surrounding, it is evident that the dykes were not made by a volcanic
eruption which forced the kimberlite through opposing strata of the
earth's crust, but either existed prior to the filling, as open chasms,
or the earth's crust was rent apart and the cavity simultaneously
filled. A local volcanic upheaval of sufficient force to break a large
funnel through thousands of feet of the earth's strata, would not stop
placidly when it reached the surface, but would have scattered evidence
of its eruption far and wide. No such evidence exists around the
diamond chimneys. Nothing has been discovered in the neighborhood of
the mines, suggestive of kimberlite. The Karoo strata are overlaid in
places by basalt, and everywhere by the red clay and calcareous tufa,
neither of which could be altered kimberlite, and in these deposits are
no diamonds nor the minerals which accompany the diamond.
Having
these facts in mind, it appears possible that in some past age there
was a tremendous derangement of the earth's crust extending from the
Bokkeveldt mountains at the Cape of Good Hope, far to the north, so
extensive in area, and by a force so evenly distributed, that the
strata of the plateau within the boundary walls maintained their
natural horizontal trend in general, and which by the spreading of its
surface, rent it in places and occasioned the huge funnel-like chasms
now known as the diamond chimneys.
It is noticeable that all diamond fields of importance are within 300 north and south of the equator. They
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