62 FLUORSPAR DEPOSITS OF SOUTHERN ILLINOIS, [bull. 253. 



tlisHeminated. Large bodies in unaltered limestone are especially 

 characteristic of the Mississippi Valley and they show throughout 

 the world a tendency toward segregation in dolomite and limestone. 

 The lead and zinc deposits found at other points in the Mississippi 

 Valley, excluding those of southwestern Arkansas, are believed to 

 represent concentrations from the surrounding limestone brought 

 alK)ut by the activities of ordinary meteoric water. Specifically, it 

 is believed that they represent material originally deposited in the 

 dolomites of the Cambro-Silurian and later concentrated in their 

 present situations." The evidence for this will not be reviewed here. 

 In certain particulars the ores of this district diifer from those found 

 elsewhere in the valley, and this raises a question as to the applica- 

 bility to them of the theories worked out from a study of the others. 

 These differences are as follows: 



(1) The antimony occurring in connection with the lead is found 

 elsewhere in this region only in southwestern Arkansas, where the 

 relations are entirely distinct from those normal to the Mississippi 

 Valley. The lead ores of the valley are always particularly free from 

 antimony, so much so as to class them as soft ores in distinction from 

 the western or hard ores. 



(2) The fact that the galena is slightly argentiferous is also dis- 

 tinctive. The amount of silver present is not great, but is none the 

 less large when contrasted with that found elsewhere in the region. 

 The following analyses made by Messrs. Chandler and Kimball were 

 published some years ago by Whitney,'' and indicate the amount of 

 this difference. 



Analyses of f/alena from southern Illinois. 



Troy ounces silver per 

 2,000 pounds lead. 



Rosiolare, 111 9^ 



Massac County, 111 1| 



Mineral Point, Wis ^ 3 



Rockville, Wis J 



Marsden lode (near Galena), 111 ^i^ 



The amount of silver is small and its occurrence seems irregular, 

 but that it is ever present to the amount indicated is striking. H. A. 

 Wheeler has recently discussed this point in connection with the 

 occurrence near Fredericktown, Mo., and in Algonkian felsites of a 

 narrow vein of nonargentiferous galena.<^ He argues from this that 

 the neighboring lead deposits in the limestone were deposited by 

 ascending waters of presumablj^ deep-seated origin. If it prove gen- 



" Preliminary report on lead and zinc deposits of the Ozark region : Twenty-second 

 Ann. Rept. U. S. Geol. Survey, pt. 2, pp. 23-227. 



" Whitney, J. D., Geol. Survey Illinois, vol. 1, 1S66, pp. 188-189. 

 •= Wheeler. H. A., Eng. and Min. Jour., March 31, 1904. 



