THEORIES OF OEE DEPOSITION HISTORICALLY 

 CONSIDERED. 



I5V S. F. EiMMONS.a 



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

 which is designed to connnemorate the peaceful acquirement a cen- 

 tury ago of the rights of France to the Mississip2:)i Valley and the 

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

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

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

 does, an amount about ecjual to the original })urchase ])rice. To a 

 still greater degree has the unexamjded rajiidity with which, 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 resoiwces — a development to which geological science 

 has in no small measure contributed. 



In selecting a sul)ject for my address as president of the (ieological 

 Society of America 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 whicli 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 scojie has been 

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

 has l)ecome little more than a brief enumeration of the opinions held 

 from time to time within the histoi'ic 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 hardly 



« Annual address liy tho president of the Geological Society of America, read 

 before the society at St. Louis, Mo., December 30, TOO:}. Keprinted from author's 

 revised copy. 



309 



