Ch. 1: Diamonds

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	UNITED STATES, CANADA AND MEXICO 33

	in the neighborhood to examine the steep slopes where gems that had weathered out of the peridotite might be exposed. Particular attention was directed also to the study of the solid rock and residuary deposits which so closely resemble the diaman-tiferous material of South Africa. Till this time the actual contact of the peridotite and shale had not been observed. It is exposed in the bed of a branch of Ison's Creek, within ioo yards of Charles Ison's house. The intrusion of the peridotite has displaced and greatly fractured the shale, besides locally indurating it and enveloping a multitude of its fragments. The latter are dark-colored, like the peridotite, and are strongly contrasted with the light-colored dolomite nodules of secondary origin. Besides pyrope garnets, a few of which are suitable for cutting, several fairly good specimens of pyroxene were found here, resembling the same transparent mineral from Arizona. The South African mineral is a little more opaque, but of a richer green color. When suitably prepared, they will make worthy additions to the gem collection of the United States National Museum. An altered biotite also occurs, identical with the South African vaalite. During a careful search over a small area for nearly two days, no diamonds were found, but this by no means demonstrates that they are not there. The similarity between the peridotite here and that of the Kimberley and other diamond mines of South Africa is very striking; and when this fact alone is considered, the probability of finding diamonds in Kentucky seems correspondingly great; but when it is noted that the carbonaceous shale, and not the peridotite itself, is the source of the carbon from which the diamond is formed, and that the shale in Kentucky is much poorer in carbon than that of South Africa, the probability is proportionally diminished. Recent excavations have shown that large quantities of this shale surround the South African mines, and that they are so highly carbonaceous as to be combustible, smouldering during long periods of time when accidentally fired. In the chemical laboratory of the United States Geological Survey, J. Edward Whitfield found 37'52 per cent, of carbon in the shale from near the Kimberley Mine, while in the blackest shale adjoining the peridotite of Ken-

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