ORES DEPOSITED BY AQUEOUS SOLUTIONS. 1061 



As further evidence of the deposition of ores from aqueous solutions 

 we may now pass to illustrations of ore deposits that exhibit phenomena 

 identical with those which are known to be produced as a consequence of 

 the action of aqueous solutions. 



Upon the point that the iron ores are dominantl y produced by the 

 circulation of ordinary meteoric waters, there is no difference of opinion; 

 there is general agreement also that these waters are mostly descending 

 waters at ordinary temperatures. (See pp. 1193-1197.) The importance 

 of waters of meteoric origin at ordinary temperatures in the genesis of ores 

 should perhaps be emphasized. Probably the iron ores preponderate in 

 volume over all other metallic ores. In the United States, Great Britain, 

 and Germany 66, 000,000 tons of iron ore were mined in the year 1902. 

 It is not probable that this amount is approached by the remaining* metallic 

 ores. Not only do the iron ores occur in largest quantity, but iron is a 

 metal of dominant importance. There is no question that the world could 

 spare all the other metals better than it could spare iron. If it be agreed 

 that iron is more important to the advancement of the race than all other 

 metals, and that iron ore occurs in greater quantity than all other ores and 

 is dominantly deposited by meteoric waters at ordinary temperatures, it 

 follows, disregarding the manner of the deposition of any other metals, 

 that the work of meteoric waters at ordinary temperatures is the most 

 important factor in metallic ore deposition. 



Other metals also are dominantly deposited by aqueous solutions. 

 Many ore deposits are so associated with the general process and the belt 

 of cementation that one must hold that the work of cementation and the 

 deposition of ores were simultaneously caused by the same agent. For 

 instance, the San Juan tuff of Colorado, a Tertiary volcanic formation, at 

 the time of its deposition must have been exceedingly porous. It is now 

 so thoroughly cemented by quartz and other gangue minerals that the 

 microscope can discover no openings. In the cementation of this tuff 

 formation an immeasurably greater quantity of material was deposited 

 between the fragments than is now found in the veins. The filling of the 

 intersecting veins contains the same gang-ue minerals as those which cement 

 the tuffs. It is perfectly clear that the formation of these veins was an 

 incident in the general process of cementation. In some of the veins, and 

 to a variable extent in the same vein, a sufficient amount of mineral was 



