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III.—On some Rock-Specimens from Kimberley, South Africa

Published online by Cambridge University Press:  01 May 2009

T. G. Bonney
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Extract

Although not strictly in the order of the title, we may describe of first a specimen from the so-called “melaphyre,” which forms a great sheet high up in the group through which the diamondbearing pipes have been driven. This, which bears the label “No. 5, Melaphyre,” is nearly 5″ in length. Macroscopically, it may be described as a compact dark basalt, showing slight signs of decomposition, and containing rather sparse amygdales of irregular size and shape (the maximum length being about half an inch), filled mostly with calcite and spotted occasionally with dark-green.

Type
Original Articles
Information
Geological Magazine , Volume 4 , Issue 11 , November 1897 , pp. 497 - 502
Copyright
Copyright © Cambridge University Press 1897

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References

page 500 note 1 Geological Magazine, 1895, p. 500.Google Scholar

page 500 note 2 The 2 in 1,200 is damaged, and may be a higher figure.

page 501 note 1 GEOL. MAG. 1895, p. 501.Google Scholar

page 501 note 2 It must be remembered that pyroxenite, troktolite, and gabbro are frequently found associated with peridotites and are generally intrusive in them.

page 501 note 3 That graphite, cliftonite, carbonado, and diamond occur in the native iron, is, of course, well known: see Fletcher, , Min. Mag., vii, 121.Google Scholar Meteorites vary from almost pure native iron to peridotites: see Wadsworth, , “Lithological Studies,” ch. ii,Google Scholar and Crookes, , Nature, lvi, p. 325. Native iron is well known to occur in some basalts.Google Scholar

page 501 note 4 According to Sir W. Crookes, F.R.S., “The Diamond Mines of Kimberley” (Lecture at Imperial Institute), the section is as follows: (1) soil, (2) basalt, much decomposed, 20′–90′, (3) black shale (combustible), 200′-250′, (4) “melaphyre,” about 400′, (5) quartzite, about 400,′ (6) variable shales.

page 502 note 1 The largest must be about 450 yards in diameter. Some of the necks in Scotland are considerably larger than this. See Sir Geikie's, A. “Ancient Volcanoes of Great Britain,” chs. xxv and xxxi.Google Scholar