THE GENESIS OF OliES 535 



Copper, lead, zinc, tin, silver and gold, although metals of great 

 importance to man, constitute so small a part that their percentages 

 are expressed by four to eight decimals, that is, between hundred 

 thousandths and billionths of a per cent. 



In some eruptive rocks, however, the percentage is much higher, 

 and has been determined to be in the thousandths of a per cent, in 

 the case of copper, lead and zinc, and one tenth to one hundredth as 

 much of silver and gold. 



The amount of metallic content found to occur as a primary 

 constituent in unaltered rock is thus seen to be far too small to con- 

 stitute workable ores, and indeed is often so insignificant as to be 

 determined with difficulty. You all know that several per cent, of 

 iron, manganese, zinc, lead and copper are required to make an ore 

 valuable, the percentage varying, of course, with the locality, com- 

 plexity of the ore and other familiar factors. 



It is therefore apparent that a process of natural concentration is 

 essential for the production of ore deposits, bringing into limited space 

 the material formerly disseminated through ten thousand or a hun- 

 dred thousand times that extent of ground, or accomplishing the same 

 result by the removal of the admingled rock impurities. 



Wherever this concentration is brought about by assembling of 

 solid particles under conditions that admit of freedom of movement, 

 we have placer deposits as of gold and platinum, of tin, iron and 

 chromium ores, and sometimes of precious stones, such as diamonds, 

 sapphires, rubies, garnets and others. 



The ores found in veins, in disseminations throughout the rocks 

 and in irregular shaped deposits in soluble rocks can not have been 

 collected in any such manner. Their mode of occurrence and relation 

 to the enclosing rocks make it evident that they have been slowly 

 deposited from solution. And the only solvent of general distribution 

 is water, with its varying content of acids and alkalies under changing 

 conditions as to temperature and pressure. 



Water is the magic instrument by which all the copper in Butte's 

 vast mines, all the gold and silver of the Comstock and of G-oldfield, 

 were assembled; more potent than the Philosopher's Stone, more uni- 

 versal than the air we breathe; constantly at work, dissolving, trans- 

 porting and redepositing. With indefatigable zeal and never-flagging 

 industry it searches through the innermost recesses and penetrates the 

 most closely locked chambers of the rocks, removing treasures through 

 their very walls, and often repairing breaches made in the attack so 

 skilfully as to defy detection, or to make the masonry stronger than 

 when first laid. Small wonder that the ancients regarded it as one of 

 the four prime elements ! 



But, although for several years water has been recognized as the 



