Abstract
LONDON
Geologists' Association, April 4. - Professor Morris, F.G.S., vice-president, in the chair.—“On the Diamond Fields of South Africa,” by Mr. G. C. Cooper.—The theory of an igneous action upon the spot at which the diamonds are now found being the explanation required to solve the problem of their origin was opposed by the author, who adduced facts from his observation in support of the opposite conclusion. He did not consider that the numerous trap dykes which characterise the South African Diamond Fields broke through the present surface, which, on the contrary, had been produced by the accumulation of materials brought by aqueous agency subsequent to the volcanic action which gave rise to the dykes. These materials consisted of a surface layer of red sand overlying a bed, from five to seven feet thick, of fragments of “lime and clay stone;” and beneath this the diamantiferous marl or “stuff” is reached. Steatitic or magnesian matter forms a considerable proportion of the “stuff” which it was contended may have been brought from magnesian rocks at a considerable distance by wafer and possibly by ice action, and deposited in the hollows formed by the trap dykes, and that these magnesium rocks may have been the original matrix of the diamonds.—“On some Fossils from the Chalk of Margate,” by J. W. Wetherell. The author had devoted some time and attention to the exploration of the chalk in the immediate neighbourhood of Margate, and had obtained, as a result, a large number of species of fossils, a list of which was given, with remarks as to relative abundance. In addition to many genera usually abundant in the upper Chalk, Behmintdla appears to be well represented in the Margate chalk, and ammonites are also found; but perhaps the most abundant fossil is the Coscinopora globularis, which varies in size from that of a walnut to a pin's head. Crystals of selenite were found as well as concretions of iron pyrites, but minerals are by no means common in the chalk of Margate.
Article PDF
Rights and permissions
About this article
Cite this article
Societies and Academies . Nature 7, 474–476 (1873). https://doi.org/10.1038/007474a0
Issue Date:
DOI: https://doi.org/10.1038/007474a0