780 



DYNAMICAL GEOLOGY. 





ently connected with the volcanic action along the coast region. This 

 ore of mercury occurs distributed in an irregular way through partially 

 altered sandstones, feebly metainorphic slates, serpentine, and hard 

 siliceous beds of Cretaceous age, all of which rocks indicate the action 

 of hot waters. The vapors of mercury were probably from beds in- 

 tersected at shallow depths by the fissures. 



In miners' language, a reef is any body of rock that yields valuable 

 ore ; and the silver-yielding beds above described are accordingly so- 

 called. The term is of Australian origin, and was first used for veins 

 of gold-bearing quartz. 



(6.) Sediment-formed Veins. — Fissures have sometimes become 

 filled from above with sand or gravel. Near Astoria, Oregon, occur 

 several large sandstone veins of this kind. (Author's Expl. Exp. 

 Rep., p. 655.) In Southern Utah and in Colorado, according to J. S. 

 Newberry, such veins exist made of coarse gravel and stones ; but the 

 stones have become coated with argentiferous galenite and other ores, 

 including silver chlorid, and the veins are worked for silver. 



At Leadville, Colorado, deposits of lead-carbonate, silver-chlorid, etc., lie on lime- 

 stone underneath porphyritic lava. They probably correspond to a contact-vein, made 

 at the time of eruption of the porphyry by means of ascending vapors and hot springs. 



By the methods which have been pointed out, the different parts of a lode, whether 

 an infiltration or contact vein, may be made to differ much from one another. The 

 upper part may have its metals indifferent states of combination from the lower, through 

 mineral solutions received from above, or those made b} r decompositions in progress, 

 and also through the direct action of atmospheric influences. The copper ore of a vein 

 may be simply chalcocite (Cu 2 S) below, and above contain, besides this species, bornite 

 (Cu 3 Fe S 3 ), chalcopyrite (Cu Fe S 2 ), copper sulphates, carbonates, phosphates, or arsen- 

 ates, and red or black copper oxyd (Cu 2 O or Cu 0) A silver mine may be long worked for 

 its chlorid and bromid of silver, and these ores fail below. A lead mine may for a 

 considerable depth yield lead carbonate, or sulphate, or phosphate, when galenite (PbS) 

 in the lead ore below. The pyrite which is so generally present in ore deposits helps 

 much in these changes, because of its own liability to change, and adds also, through 

 its ox} r dation, to the red or brown iron oxyd formed, if not the only source of this 

 oxyd (p. 704). 



Much light has been thrown on these transformations by various experimenters, and 

 especially by Bischof and Daubree. Daubre'e found, in the thermal waters at Bour- 

 bonne-les-Bains (department of Haute-Marne, France), in the bottom of a part of which, 

 in Roman times, bronze, silver, and gold coins had become buried, the following min- 

 eral species, which he proved to have been derived from the alteration of the metal of 

 the first two of these kinds of coins through the agency of the mineral waters, the tem- 

 perature of which is 140° F. : the copper ores, chalcolite, chalcopyrite (copper pyrites), 

 bornite, tetrahedrite, atacamite, cuprite (red oxyd of copper), chrysocolla, native cop- 

 per ; the lead ores, cerussite (lead carbonate), anglesite (lead sulphate), galenite, phos- 

 genite, and pyrite. All these species came from the action of the same water, at a com- 

 paratively low temperature. The bronze was found to consist of copper, tin, and lead, 

 or of copper and zinc, with a trace of iron. The materials obtained in the analysis of 

 these waters are chlorids and sulphates of the alkalies and of lime and magnesia, with 

 bromids, and carbonates of lime and iron, an alkaline silicate, besides traces of arsenic, 

 manganese, iodine, boron, lithia, strontia, caesium, rubidium, and, in exhalations, some 

 sulphuretted hydrogen, nitrogen, and oxygen. 



Similar results were observed b}" Daubree at the warm springs of Plombieres, Depart- 



