96 THE NATURALIST IX NICARAGUA. [Ch. VI. 



Mr. David Forbes,* in his account of the gold of Peru 

 and Bolivia, has advanced the opinion that auriferous 

 quartz veins belong to two different systems, one occur- 

 ring in connection with Granitic, the other with 

 Diorytic intrusive rocks. In later papers he has shown 

 that this occurrence of gold is not confined to South 

 America, but appears to prevail in all the other quarters 

 of the world. f One of the latest writers on the subject, 

 Mr. R. Daintree, in his "Notes on the Geology of 

 Queensland," has shown that the auriferous veinstones 

 in that colony occur in connection with, or in the near 

 vicinity of certain intrusive trap-rocks, and that even 

 some of the trappean dykes themselves are auriferous. J 

 I, myself, several years ago, endeavoured to show that 

 mineral veins in granitic districts occurred in regular 

 sequences, with certain intrusive rocks, as follows : 

 1st, Intrusion of main mass of granite ; 2nd, Granitic 

 veins ; 3rd, Elvan dykes ; and, lastly, Mineral veins, 

 cutting through all the other intrusive rocks. Later 

 observations have led me to conclude that a similar 

 sequence of events characterised the occurrence of 

 auriferous quartz veins in connection with the intrusive 

 rocks, commonly designated Greenstones, in some 

 districts consisting of diabase, as in North Wales, near 

 Dolgelly ; in others of dioryte, as in Santo Domingo ; 

 and in many parts of South America and Australia. 

 In North Wales we have, firstly, an intrusion of diabase, 

 occurring in great mountain masses ; 2ndly, Irregular 



* Quar. Joum. Geol. Soc. , Vol. xvii. 



4* Geological Magazine, September, 18C6. 



J Quart. Journ. Geol. Soc. , Vol. xxviii. p. 308. 



See " Geol. Survey of Canada," pp. 141 and 173. 



