ECONOMIC GEOLOGY 467 



be noticed that the percentage of sulphur present is 

 very low indeed. 



From the results of numerous tests on the railways 

 it has been found that the average weight of water 

 evaporated at and from 212 F. in an engine boiler per 

 pound of coal burnt is 5'0 in the case of Stormberg coal, 

 and 5'5 in the case of Indwe coal, as compared with 7 "5 

 in the case of Welsh coal. 



The annual output from the Indwe and Stormberg 

 collieries has been usually close upon 200,000 tons, the 

 former contributing a little more than 60 per cent. 



A material allied to torbanite (oil shale) occurs below 

 a coal seam in Matatiele. 1 



Copper. All the copper ore raised in the Colony 

 comes from Namaqualand, the important mines being 

 the O'Okiep, Spectakel, Nababeep, Tweefontein and 

 O'Okiep East, all in the neighbourhood of O'Okiep ; 

 most of these have been worked for some considerable 

 period. 



The ore is principally bornite with a lesser amount 

 of copper-pyrites, and occurs in dykes of an igneous 

 rock varying in composition from norite to hypersthen- 

 ite and cutting across the gneiss in a nearly east and 

 west direction. 2 The bornite is either disseminated 

 through the dyke material or is collected together to 

 form great masses, "pockets" as they are termed. The 

 most remarkable feature is that the bornite appears to 

 be one of the constituents of the hypersthene-rock, and 



1 G. C., vii., p. 21. 



2 J. H. Ronaldson, T. G. S. S. A., viii., p. 158. 



30* 



