034 RECORD OF MEETINGS OF THE 



thing that modern processes chiefly differ from those of the 

 ancients. 



Of all the metals the most important which minister to the 

 needs of daily life are the following, ranged as nearly as possible 

 in the order of their usefulness: Iron, copper, lead, zinc, silver, 

 gold, tin, aluminum, nickel, platinum, manganese, chromium, 

 quicksilver, antimony, arsenic, and cobalt. The others are of 

 very minor importance, although often indispensable for cer- 

 tain restricted uses. 



The manner of occurrence of these metals in the earth, and 

 their amount in ores which admit of practicable working, are 

 fundamental facts in all our industrial development, and some 

 accurate knowledge of them ought to be a part of the intellectual 

 equipment of every well-educated man. The matter may well 

 appeal to Americans, since the United States have developed 

 within a few years into the foremost producer of iron, copper 

 lead, coal, and until recent years in gold and silver; but with 

 regard to gold, they have of late alternated in the leadership 

 with the Transvaal and Australia, and in silver are now second 

 to Mexico. 



Despite the enormous product of food-stuffs, American mining 

 developments are of the same order of magnitude; and the 

 mineral resources of the country have proved to be one of the 

 richest possessions of its people. 



We may best gain a proper conception of the problem of the 

 metalliferous veins if we state at the outset the gross composi- 

 tion of the outer portion of the globe, so far as geologists have 

 been able to express it by grouping analyses of rocks. We 

 may then note among the elements mentioned such of the metals 

 as have just been cited and may remark the rarity of the others; 

 we may next set forth the necessary percentages of each metal 

 which make a deposit an ore, that is, make it rich enough for 

 profitable working. By comparison we can grasp in a general 

 way the amount of concentration which must be accomplished 

 by the geological agents in order to collect from a naturally 

 lean distribution in rocks enough of a given metal to produce 

 a deposit of ore; and can then naturally pass to a brief discus- 

 sion and description of those agents and their operations. 



