ORES DEPOSITED BY AQUEOUS SOLUTIONS. 1059 



First, it has been shown (pp. 571-572, 612-640) that the general 

 cementation of the belt so named is due to the work of underground water. 

 The evidence upon this point is briefly summarized in this chapter. (See 

 pp. 1024-1028.) If general cementation is correctly attributed to deposi- 

 tion by underground water, it can hardly be doubted that many ore deposits 

 are due to the same agency, since in general the majority of ore deposits differ 

 in no essential respect from the ordinary cementation products, except that 

 they contain an unusual amount of certain metals of importance to man. If 

 underground water carried and deposited the material in the openings of 

 sand, transforming them to sandstones and quartzites, in the larger openings 

 of conglomerates and great tuff formations, thus indurating them, and in the 

 innumerable openings produced by joint, fault, bedding parting, and brecci- 

 ation fractures, it follows that similar deposits containing a minute fraction 

 of a per cent of gold or silver, a small amount of copper, or a large quantity 

 of iron — in other words, ores — are also the results of aqueous deposition. 

 However, evidence that the majority of ores are deposited by underground 

 waters does not rest alone upon the general argument of cementation. 



The second argument in favor of the deposition of the majority of ores 

 by aqueous solution is the nature of the accompanving- gangue minerals 

 and their relations to the ores. The gangue minerals which accompany 

 the great majority of veins are the hydrous silicates, including- kaolinite, 

 sericite, the zeolites, and chlorites ; the carbonates, such as calcite, 

 dolomite, and siderite; and the oxides, such as quartz and hematite. In 

 other words, the dominant gangue minerals are the identical ones produced 

 on an extensive scale by metasomatic processes within the belt of cementa- 

 tion, and deposited upon a grand scale in the openings of that belt, thus 

 cementing the rocks. 



But the conclusion that such minerals are deposited from aqueous 

 solutions does not depend upon their likeness to the minerals of the belt 

 of cementation. Actual observations show that these minerals are now 

 being deposited by aqueous solutions. This has been observed at various 

 places. In this country the most famous localities are Sulphur Bank, 

 California, Steamboat Springs, Nevada, and the Yellowstone Park. 

 Perhaps the best-studied instance of all is that of Boulder Hot Springs, 

 Montana, where the vein deposits and the alterations of the accompanying- 

 rock have been recently very closely examined and well described by 



