16 



SCIENCE. 



[N. S. Vol. XXIII. No. 575. 



enough of a given metal to produce a de- 

 posit of ore; and can then naturally pass 

 to a brief discussion and description of 

 those agents and their operations. 



If the general composition of the crust 

 of the earth is calculated as closely as pos- 

 sible on the basis of known chemical anal- 

 yses, the following table results, which has 

 been compiled by Dr. F. W. Clarke, of 

 Washington, chief chemist of the U. S. 

 Geological Suryey.^ 



Oxygen 47.13 



Silicon 27.89 



Aluminum 8.13 



Iron 4.71 



Calcium 3.53 



Magnesium 2.64 



Potassium 2.35 



Sodium 2.68 



Titanium 32 



Hydrogen 17 



Carbon .13 



Pliospliorus 09 



Manganese 07 



Sulphur 06 



Barium 04 



Chromium 01 



Nickel 01 



Strontium 01 



Lithium 01 



Chlorine 01 



Fluorine 01 



Total 100.00 



Elements less than .01 per cent, are not 

 considered abundant enough to affect the 

 total, and equally exact data regarding 

 them are not accessible. Among those 

 given only the following appear which are 

 metals of importance as such in every-day 

 life: aluminum 8.13, iron 4.71, manganese 

 .07, chromium .01 and nickel .01. They 

 rank, respectively, in the table, third, 

 fourth, thirteenth, sixteenth and seven- 

 teenth. Of the five, iron is the only one of 

 marked prominence. No one of the re- 

 niaining four is comparable in usefulness 

 with ■ at least five other metals which are 



» Bulletin 148, p. 13. 



not mentioned, viz., copper, lead, zinc, 

 silver and gold. 



An endeavor has been made by at least 

 one investigator, Professor J. H. L. Vogt, 

 of Christiania, to establish some quantita- 

 tive expression for these other metals. 

 His estimates are as follows:* 



Copper percentage beyond the fourth or 

 fifth place of decimals, that is, in the hun- 

 dred thousandths or millionths of a per 

 cent. 



Lead and zinc, percentages in the fifth 

 place of decimals or in the hundred thou- 

 sandths of a per cent. 



Silver, percentage, two decimal places 

 beyond copper — or in the ten millionths to 

 the hundred millionths of a per cent., or 

 the ten thousandth to the hundred thou- 

 sandth of an ounce to the ton. 



Gold, percentage, one tenth as much as 

 silver. 



Tin, percentage in the fourth or fifth 

 decimal place, that is, in the ten thou- 

 sandths or hundred thousandths of a per 

 cent. 



These figures, inconceivably small as they 

 are, convey some idea of the rarity of these 

 metals as constituents on the average of the 

 outer six or eight miles of the earth's crust. 

 But they are locally more abundant in par- 

 ticular masses of eruptive rocks which are 

 associated Avith ore deposits. 



In the following tabulation I have en- 

 deavored to bring together a number of 

 determinations which have been made in 

 connection with investigations of American 

 mining districts. In a general way they 

 give a fair idea of the metallic contents of 

 certain eruptive rocks from which were 

 taken samples as little as possible open to 

 the suspicion that they had been enriched 

 by the same processes Avhich had produced 

 the neighboring ore-bodies. 



In oi'der to come within the possible 

 limits of profitable and successful treat- 

 ^ Zeitschrift fiir prak. Geologie, 1898, 324. 



