534 POPULAR SCIENCE MONTHLY 



THE GENESIS OF OEES IN THE LIGHT OF MODERN 



THEORY 



By HORACE V. WINCHELL 



MINNEAPOLIS, MINN. 



IT is well understood, but often forgotten, that all the constituents 

 of ore deposits are found in some form in the earth's crust, con- 

 tained in more or less abundance in the rocks, especially in the erup- 

 tive rocks; and that they have been in some way collected from their 

 disseminated condition in these rocks, and concentrated in veins, beds 

 or other deposits. 



Analyses of fresh eruptive rocks have demonstrated the existence 

 therein of all of the ingredients of our valuable ores and their com- 

 pounds. Few of them occur native like gold, silver, copper and 

 platinum; and often, because of their minute quantity and fine state 

 of subdivision, it is not possible to determine the precise form in 

 which they are present. 



The presence of sulphur, arsenic, antimony and tellurium indicates 

 that there may be many metallic combinations in the eruptive magmas 

 similar to those formed at later periods, nearer the surface. 



The average composition of the earth's crust has been approximately 

 estimated as follows: 1 



Per Cent. 



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 



Phosphorus 09 



Manganese 07 



Sulphur 06 



Barium 04 



Chromium 01 



Nickel 01 



Strontium 01 



Lithium 01 



Chlorine 01 



Fluorine 01 



Total 100.00 



J F. W. Clarke, Bull. U. S. G. S., 148, p. 12; J. F. Kemp, Econ. GeoL, I., 

 III., 210. 



