170 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Jan. 27, 



There is abundant evidence that the latter rocks were very much 

 disturbed during the period in which they were formed ; for we 

 found the gneiss in a most contorted state, and not unfrequently 

 containing extensive developments of quartz, both in veins and in 

 lenticular forms. ISTone of these veins are ever found entering the 

 strata which succeed the gneiss and granite and rest unconformably 

 upon them. I take it that these strata are Silurian ; Bain and all 

 his Cape contemporaries thought so. They are generally horizontal, 

 but not unfrequently are flexuous, and at times so faulty that there 

 maybe a difference of even 1000 feet in the elevation of strata which 

 at one time were continuous on the same plane. 



The primitive rocks in the valleys where the gold has been found 

 have been very much eroded by the rivers : in some parts it is no 

 exaggeration to take it at 3000 feet depth ; and it is common to find 

 valleys of from 500 to 1000 feet in depth. It would appear to me a 

 reasonable assumption that no part of the gold contained in the 

 rocks that have been removed (chiefly in the form of mud and fine 

 sand) has been carried away, but that it remains in the alluvions 

 now traversed by the same rivers. Although in the parent rock 

 the quantity may be imperceptibly small, it may be found in more 

 abundant traces in the debris, which throughout an extensive valley 

 will show the course the river followed in the remotest periods of 

 its existence. The features peculiar to one river will apply to all 

 which traverse the primitive rocks ; the same action has been alike 

 effectual in all. In the faulty state of the Silurian strata to which 

 I have alluded, there is ample proof that the primitive rocks on 

 which they unconformably rest have suffered great displacement, 

 and the relative levels of many localities have been greatly altered. 

 This, no doubt, would have resulted, in the first instance, in forming 

 valleys of elevation, upon which the denuding agency, down to the 

 present time, has been operating. The point I wish to bring out is, 

 that the gold contained in the primitive rocks will be found collected 

 in the alluvions, and that hence, the amount being very small, it 

 may be imperceptible in the rocks in situ, although quite perceptible 

 in the debris along the course of the river. 



I was not able to ascertain from Mauch, when he was here some 

 months ago, whether the occurrence of the gold in the interior has 

 the same relations as in this colony, or whether it bears comparison 

 with that of the Ural, or Australia and America, where it would 

 appear to pervade the ramifications of veinstones of quartz into the 

 strata. 



Discussion. 



Mr. David Foebes was glad to find that Dr. Sutherland corrobo- 

 rated his views as to the occurrence of gold in two ways : — 



1. In auriferous granite, as in Wicklow and elsewhere. 



2. In eruptive diorite, a basic rock without free quartz, and cer- 

 tainly of postoolitic date, almost always accompanied by copper- 

 veins. Most Californian gold- veins are connected with this class 

 of rocks. 



