DIAMOND-FIELDS OF SOUTH AFEICA. 883 



auriferous reefs are worked. The containing rock is steatitic and 

 chloritic schist, dipping at a angle of about 80° to the northward. 

 This series rests on gneiss, and is overlain unconformably by the 

 group of beds in which gold occurs at Lydenburg. The principal 

 reef worked is called the " Natalia," about 3 feet wide in places, 

 dipping about 80° to northward (fig. 5) ; some very rich patches have 

 been met with in it ; and a fair sprinkling of gold runs throughout 

 the stone ; it is in the solid quartz as well as in the cavities. Dj^kes 

 of diabase run east and west, parallel and close to the reef; cross 

 dykes of dolerite intersect it. 



Numerous other reefs run parallel and at right angles to the 

 " Natalia." Some of them are auriferous ; but so far none of them 

 have been sufficiently explored to determine their value. Extensive 

 crushing- plant has been erected at Eersteling ; the yield from the 

 main reef has been less than 1 ounce of gold per ton of quartz. 



At Marabastadt the schistose series includes beds of green talcose 

 schist, quartz rock, and felspathic schist, standing at high angles. 

 Veins of quartz bearing N.E. run between the bedding ; much of 

 this quartz is cherty in appearance, and looks more like quartz rock 

 than vein- quartz. Several of these veins contain gold in the heart 

 of the quartz, but nothing payable has been discovered. Outliers of 

 schist, containing reefs of quartz, crop out in several places over the 

 gneiss- country, N. of 24° S. lat. Gold is reported as occurring in 

 some of them. 



III. Cobalt. 



Smaltite and erythrite occur in the Transvaal, at a locality situated 

 about six miles from Oliphant River, on a small stream named Kruis 

 River. Middleburg is about thirty-six miles south. 



The rock in which the cobalt-ore occurs is very fine-grained felsite, 

 much shattered. The hanging wall of the mineral-yielding portion 

 is formed by a large dyke of very fine-grained dolerite. There is no 

 defined lode ; but about 18 inches of the felsite rock, in contact with 

 the dyke, carries small threads and lenticular veins of the ore, run- 

 ning parallel to the dyke (fig. 3) ; the widest vein of solid ore was 8 

 inches thick, but soon thinned out all round. The solid rock near the 

 contact is mineralized ; specks of ore are sprinkled through it. The 

 mineralized part strikes E. 10° S. magn., and dips 55° southward. 

 Beryls and millerite occur at the east end of the present workings ; 

 and the locality is one likely to prove rich in other minerals. To the 

 east and south is an extensive area of diorite, amygdaloid, &c. More 

 than 100 tons of ore have been sent to London. 



