Mr. David Forbes,* (* "Quarterly Journal of the Geological Society" volume 17.) 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 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 parts of the world.* (* "Geological Magazine" September 1866.) 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.* (* "Quarterly Journal of the Geological Society" volume 28 page 308.) Several years ago, I endeavoured to show that mineral veins in granitic districts occurred in regular sequences, with certain intrusive rocks, as follows:--first, Intrusion of main mass of granite; second, Granitic veins; third, Elvan dykes; and, lastly, Mineral veins, cutting through all the other intrusive rocks.* (* See "Geological Survey of Canada" pages 141 and 173.) 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; 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,* (* "Mineral Veins" page 16.) and it appears that the origin of such veins is the natural result of the plutonic intrusion. There is, also, sometimes a complete gradation from veins of perfectly crystallised granite, through others abounding in quartz at the expense of the other constituents, up to veins filled with pure quartz, as at Porth Just, near Cape Cornwall; and, again, the same vein will in some parts be filled with felspar; in others, contain irregular masses of quartz, apparently the excess of silica beyond what has been absorbed in the trisilicate compound of felspar.* (* Mr. John Phillips in "Memoirs, Geological Survey of Great Britain" volume 2 page 45.) Granitic, porphyritic, and trappean dykes* also sometimes contain gold and other metals; (* Sir R.I. Murchison "Siluria" pages 479, 481, 488 and 500; and R. Daintree "Quarterly Journal of the Geological Society" volume 28 pages 308, 310.) and I think the probability is great that quartz