1869. SUTHERLAND—AFRICAN AURIFEROUS ROCKS. 169 



4. Note on the Auriferous Eocks of South-eastern Africa. 

 By Dr. Sutherland, Surveyor-General of Natal. 



(Communicated by Sir R. I. Murchison, Bart., K.C.B.) 



In communicating the chief contents of a letter which was addressed 

 to me by Dr. Sutherland, I beg to point out to the Society that the 

 author seems to have arrived at some of the same conclusions as 

 those deduced by Mr. David Porbes from his examination of the 

 gold-bearing rocks of South America, which he described as result- 

 ing from the action of two very distinct classes of igneous rocks. 

 (See Geol. Magazine, vol. iii. pp. 385 &c., Sept. 1866). 



EoD. I. Murchison. 



Natal, South Africa, Sept. 8th, 1868. 



A young man of the name of Parsons, who made a journey 

 with me in March last along the southern rivers of this colony, 

 washed some iron -sand, which gave distinct traces of gold. Since 

 his discovery several persons have also succeeded in finding traces 

 by the same means ; but in no case has it been found in remu- 

 nerative quantities ; the particles never exceed the tenth or twen- 

 tieth part of a grain in weight ; the form is rounded and pitted, 

 very much the same as the Australian " pepitas," or nuggets, but 

 visible only with a magnifying power. 



Parsons has been temporarily employed by the Government to ex- 

 plore the rivers, with a view to settle the question whether or not 

 the metal exists in such quantities as will pay labouring men fair 

 wages while employed in its extraction. 



I have gone carefully over chap. xix. of your fourth edition of 

 * Siluria ;' and the conclusion to which I am driven is this, — that 

 the noble metal is in such a state of diffusion among the gneiss and 

 granite (for these are the rocks that yield it) as to be imperceptible 

 to the eye, and not in any way occurring in ramifications and small 

 veins. You will recognize Humboldt's words as you give them at 

 page 474. 



In no part of the South-African promontory that I know do the 

 hypogene rocks protrude into the Secondary formations. It is true 

 we have a most abundant development of erupted rock, chiefly 

 basaltic greenstone, which has pierced all the strata except the 

 small patches of " chalk." Bain's Dicynodon-strata, which contain 

 the coal, are abundantly impregnated with it. In one locality, the 

 Insizwa Mountains in the basin of the St. John's River, its mineral 

 character seems to resemble diorite ; and there, along the line of 

 contact with the Secondary strata, it contains various ores of copper, 

 which have been found to contain about 100 grains of gold to the 

 ton of ore. But this basaltic rock is much more recent than the 

 basaltic rock we found in the primitive rocks ; the latter appear to 

 have settled down into perfect repose when the Palaeozoic strata 

 were undergoing a succession of invasions from eruptions of igneous 

 matter, which in no instance assumes the type of the granitic or 

 gneissose rocks. 



