76 The Naturalist in Nicaragua 
been achieved in some places, and a regular ‘“‘ Manto” pro- 
duced. I have already stated that small landslips are of 
frequent occurrence on the sides of the hills. We had several 
times the entrance to our mines temporarily closed by them 
in the wet season. : 
Mr. David Forbes,’ in his account of the geology of Peru 
and Bolivia, has advanced the opinion that auriferous quartz 
veins belong to two different systems, one occurring in con- 
nection 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 
parts of the world.” 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.? Several years ago, I 
endeavoured to show that mineral veins in granitic districts 
occurred in regular sequences, with certain intrusive rocks, 
as follows:—u1st, Intrusion of main mass of granite; 2nd, 
Granitic veins; 3rd, Elvan dykes; and, lastly, Mineral veins, 
cutting through all the other intrusive rocks.* Later ob- 
servations 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 ; 
secondly, Irregular tortuous dykes of diabase; thirdly, Elvan 
dykes; ‘and, lastly, auriferous quartz veins. ‘In every region 
of intrusive plutonic rocks that has been thoroughly explored, 
a similar succession of events, culminating in the production 
of mineral veins, has been proved to have taken place,® and 
it appears that the origin of such veins is the natural result 
of the plutonic intrusion. There is, also, sometimes a com- 
* Quart. Journ. Geol. Soc., vol. xvii. 
* Geological Magazine, September 1866. 
3 Quart. Journ. Geol. Soc., vol. xxviii. p. 308. 
#See Geol. Survey of Canada, pp. 141 and 173. 
5 Mineral Veins, p. 16. 
