USEFUL METALS 



reaching the Jopl'm district is through the lead and zinc-bearing calcar- 

 eous formations, render it reasonably certain that these formations are 

 the source of the ore bodies." 



The immediate source of the ores is the various limestones 

 situated below the Pennsylvania!! terranes. 



The method of mining at Joplin is peculiar to that district 

 alone. The land holder leases the property for ten years for a 

 royalty of 8 per cent, to 15 per cent, of the gross value of the out- 

 put. The leasee prospects by drilling and sinking shafts, by 



m- 



FIG. 131. View near Linden in Wisconsin lead and zinc district. (By 

 permission of the Macmillan Company, from Ries' Economic Geology.) 



cross cutting and drifting, and then subleases for a royalty of 

 from 15 per cent, to 25 per cent, of the gross output of the ores. 

 Three results are said to have followed this method. 1. The dis- 

 covery of many new ore bodies. 2. Freedom from serious labor 

 troubles. 3. Increase in the annual output of zinc, so that the 

 Joplin district has become the premier area of the world (Fig. 130). 

 Other important districts are located in Wisconsin, Arkansas, 

 Kentucky and Illinois. (See Fig. 131.) 



3. Cordilleran Region. In the Cordilleran district the best rep- 



