PRECIOUS STONES.	107
	on the farm of Du Toit's Pan led to the opening up of the mine now known by that name, and soon there was a rush. This discovery was followed by another close by, on the site now occupied by Kimberley; this was the famous De Beers' mine. In all there are now four large deposits close to the town. Two other deposits were also found south-south-east of Kimberley, namely, the Koffyfontein and Jagers-fontein mines, in what is now the Orange Eiver Colony. A very important deposit has more recently been found at the New Premier mine, near Pretoria, from which the famous Cullinan Diamond was obtained. There was little on the surface to mark the position of these deposits around Kimberly; some of them were slightly raised above the surrounding country, some showed a slight depression. When they came to be worked, however, it was soon seen they were anything but surface deposits, as at first supposed, for the material in which the Diamonds were found was utterly unlike the neighbouring rock, from which, moreover, it was separated by a sharp line of demarcation. This surrounding rock consists of beds of the Karoo forma­tion. Under a layer of reddish earth is a bed of calcareous tufa which has evidently been deposited long subsequent to the formation of the material in which the Diamonds are found, and therefore, too, later tban the Karoo beds, which are themselves of comparatively recent geological age, belonging as they do to the time of the New Bed Series. The Karoo beds, as seen in the Kimberley mine, consist of a layer of shale, varying in colour from a greenish tint above to yellowish below ; an intrusive sheet of dolerite of late Karoo age follows, and with the shales makes up a thick­ness of 50 feet. Below this comes a bed of black shales