THEORIES OF ORE DEPOSITION HISTORICALLY 

 CONSIDERED. 



P.v S. F. Emmons.o 



111 the city in which we meet this year an exposition is preparing 

 which is designed to coniineinorate the peaceful acquirement a cen- 

 tur}^ ago of the rights of France to the Mississippi Valley and the 

 regions to the west. It was the metallic wealth of the valley region 

 Avhich first led to its exploration by the French, and which still con- 

 stitutes an important feature in its industry, yielding annually, as it 

 does, an amount about equal to the original purchase price. To a 

 still greater degree has the unexampled rapidity \tith w'hich, in the 

 last half century, civilization and industry have spread over the 

 mountainous regions of the West been due to the development of 

 their mineral resources — a development to which geological science 

 has in no small measure contributed. 



In selecting a subject for my address as president of the Geological 

 Society of xVmerica it has seemed appropriate, therefore, both to the 

 time and to the place, to choose a theme that has to do with that 

 branch of geology which is especially concerned with the deposits 

 of the metals. The history of theories of ore deposition was the sub- 

 ject originally chosen, but, as it gradually developed in the course 

 of research, it was found that anything worthy of that name would 

 far exceed the proper limits of an address. Thus its scope has been 

 gradually narrowed to fit the necessities of the occasion, until it 

 has become little more than a brief enumeration of the opinions held 

 from time to time within the historic period which seems to have 

 left the most permanent impress upon the minds of geologists. 



The term " ore deposition," which is used in preference to its 

 earlier synonym '' vein formation " as more correctly representing 

 the broader conceptions of the present day, applies, it is hardlj'^ 



a Annual address by tho president of tbe Geological Society of America, read 

 before tbe society at St. Louis, Mo., December 30, 1903. Reprinted from author's 

 revised copy. 



309 



