Auriferous Quartz-veins. 
123 
44 6. The salts in solution in the sea-water included in the sedi- 
ments, and the materials of the sediments themselves, reacted 
upon each other under the influences of heat and pressure. 
44 7. The mineralized waters would find passage through the 
contact planes of the igneous and sedimentary rocks, and by 
fractures in the strata, &c. 
44 8. On the cooling down of the rocks, the waters would like- 
wise lessen in temperature, and deposit their metallic and mineral 
substances which they had 4 leached* out of the sediments ; 
would deposit them in the contact planes, faults, and fissures. 
Faults which had been penetrated by dykes would also afford 
passage to such waters, and to sublimations, c.g., Cohen’s Reef 
and also 4 Steam-boat Springs of California.’ 
44 9. All the saline solutions in the Paleozoic seas would enter 
into reactions, and even if the gold had beeu reduced by organic 
substances, it would, I think, be again chlorinated on the re- 
generation of the felspars out of the materials of the sediments and 
the alkaline chlorides and chloride of calcium in solution. 
44 It seems to mo, therefore, probable that we may refer the 
formation of auriferous veins and metalliferous lodes, generally 
occurring in the Silurian and Devonian formations, to Plutonic and 
volcanic action, which prevailed about the close of the Silurian 
period and omvards, until our geological record closes in the 
Upper Devonian. But we must also take into accouut a secondary 
process which is always going on in the reactions produced by 
meteoric waters percolating from the surface downward ; this 
process is partly one of decomposition and partly of concentration. 
44 The conclusions 1 arrive at are, therefore — First, that the gold 
has been collected out of the sediments during the Plutonic and 
volcanic action in Palaeozoic periods ; second, that it has been (at 
the surface) undergoing concentration, partly by the removal or 
decomposition of metallic ores. We know that auriferous reefs 
very frequently, if not almost always, occur in bands along the 
strike of the sediments. In accordance with the above views, 
I suggest that these bands represent extensive fractures, com- 
municating downwards with the planes of contact of the igneous 
and sedimentary formations. Such extensive fractures would 
give passage to heated mineralized waters and to sublimations. 
As to these bands, I think we may assulne the following: — 
44 1st. The folding and compression of the Siluriau rocks w as 
consequent upon the contraction of the earth’s crust through 
cooling of the globe. 
“2nd. That fractures 'would most probably occur along the 
axes of anticlinal and synclinal folds. 
44 3rd. The pressure of a folded and depressed portion of the 
earth’s crust upon the molten material beneath would afford a 
sufficient primum mobile to produce the upward thrust of liquid 
