Ch. 1: Diamonds of India

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	8	DIAMONDS.

	stones. The latter were in fact held to constitute the unaltered portion of the rocks of the same period. The work of the Survey has demonstrated that this clay slate, or diamond sandstone, or Vindhyan formation, is separated by a wide break in time from the fossil-bearing rocks, being itself, so far as is known, absolutely azoic, and occupying a position in the geological sequence which may range from Lower Silurian to Carboniferous. Further reference to the fossiliferous rocks will therefore be unnecessary here.* Dr. Carter arrived at the conclusion that the diamond-bearing conglomerates, described by various authorities, occurred at least in the neighbourhood of, if they did not constitute members of, the Oolite formation. If for Oolite the term Vindhyan be substituted, the conclusion is probably in the main correct, and borne out by the most recent researches. But these researches have demonstrated that the principal diamond-bearing strata of the northern and southern areas respectively occupy distinct horizons, in those cases where the beds are not merely recent or sub-recent accumulations of debris. It is due to Captain Newbold to say that he disagreed with the conclusions of many of the previous authorities, and he appears to have been inclined to regard the " sandstones " as being of Devonian age— a supposition probably not very far from the truth. The Vindhyan rocks of Northern India are separated into two formations or sets of groups, distinguished as Upper and Lower. * They will be found described in the chapter on " Coal."

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