352 ORIGIISr AND DEVELOPMENT OF ORE-DEPOSITS. 



2. The veinstones and ores of the West of England may be 

 conveniently considered as to their origin under five heads, of 

 which examples are given in the following groups : 



Group 1. — "Soluble" veinstones, as calcite. 

 ,, 2. — "Insoluble" veinstones, as quartz. 

 „ 3. — "Soluble" oxidized metallic salts, as cuprite, 



malachite and chalybite. 

 ,, 4. — "Insoluble" metallic sulphides, as pyrites, 



chalcopyrite, galena, and blende. 

 ,, 5. — Schorl and other fluorine-bearing minerals with 



oxide of tin.* 



3. All the elements contained in the substances mentioned 

 above are known to occur as rock constituents, either as oxides, 

 carbonates, sulphides, or silicates, and at such considerable 

 distances from the lode-fissures as to lead to the conclusion that 

 they existed there before the nearest lode-fissures were formed. f 



4. Forchhammer, Bischoff, Dieulefait, and others have 

 shown that the waters of the sea, in which most stratified rocks 

 have been laid down, also contain notable proportions of many 

 of the metallic and other constituents found in lodes,:]: and as 

 already stated, Bischoff, Daubree, and others have shewn the 

 existence in nautical waters of every one of the substances in 

 question, 



5. The original sources of the circulating solutions cannot 

 perhaps be determined, but as they must be constantly replenished 

 by rain water falling on the earth's surface, which is practically 

 pure (except for the presence of carbonic acid) and free from 

 all the substances referred to, we may consider the cycle of 

 changes to begin with the action of pure water on rocks 

 containing all the said substances. 



*The expressions "soluble" and "insoluble" here refer to the actions of 

 ordinary surface waters which are slightly acid. But they must not be understood 

 too literally, since even silica is found in many natural " acid " waters, though it 

 is more readily soluble in those which are alkaline. 



t This has been particularly shewn by the investigations of Sandberger, and 

 confirmed by Credner, Frick and others, although Sandberger's contention that nil 

 the metalliferous contents of the veins have been derived from pre-existing 

 silicates is by no means generally admitted. 



t Revue XJniverselle des Mines, 1880, p. 425. 



