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Sec. II, Ch. 2: The African Diamond

Sec. II, Ch. 2: The African Diamond Page of 366 Sec. II, Ch. 2: The African Diamond Text size:minus plus Restore normal size   Mail page  Print this page
African Diamonds.
79
Until the discoveries of Diamonds directed attention to this district, scarcely anything was known of its geological character. Stripped of all superficial deposits, the solid framework of the country consists of recks belonging to that great geological series which, from its conspicuous occurrence in the " karoos " or vast plains in the interior, has received the name of the Karoo-formation. For the most part it consists of shales and sandstones, which re­present old deposits of mud and sand, now hardened and altered, but originally thrown down as sediment in a vast fresh-water lake Africa is still famous for its large sheets of inland water ; but the lakes in which the karoo beds were deposited are of great geological antiquity, probably cor­responding roughly in time with the period at which the New Red Sandstone of this country was formed. Although for the most part destitute of fossils, the karoo strata are in places rich in organic remains, the most notable being the relics of extinct reptiles, which must have lived near the margin of the waters which deposited the ancient sediment.
In addition to these remains of extinct animals, we find in many of the karoo-beds numerous vegetable relics, in some places in the form of fossil-wood, while elsewhere the wood has been converted into coal. The coal seams of the karoo series occur especially in the upper part of the formation, and notably at the Stormberg. By the action of heat, some of the Stormberg coal has been converted into anthracite or steam-coal, a variety of fossil-fuel peculiarly rich in carbon ; whilst the occurrence of graphite, or " black-lead," in some of these beds, has been regarded as the result of further modification of the coal. As graphite is but an impure variety of carbon, whilst we know that the Diamond is simply a pure crystallized form of the same element, some geologists have been tempted to
Sec. II, Ch. 2: The African Diamond Page of 366 Sec. II, Ch. 2: The African Diamond
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