the rainy season, evaporates during the dry months, only one of them holding water throughout the dry season. The rocks which surround the craters are capped by red soil or calcareous tufa, and in places by both, the red soil covering the tufa.
The diamantiferous breccia filling the mines, usually called " blue ground," is a collection of fragments of shale, various eruptive rocks, boulders, and crystals of many kinds of minerals. Indeed, a more heterogeneous mixture can hardly be found anywhere else on this globe. The ground mass is of a bluish green, soapy to the touch and friable, especially after exposure to the weather. Professor Maskelyne considers it to be a hydrated bronzite with a little serpentine.
The Kimberley mine is filled for the first 70 or 80 feet with what is called " yellow ground," and below that with "blue ground'' (Fig. 4). This superposed yellow on blue is common to all the mines. The blue is the
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