SCHMIDT 



-LEAD AND ZINC DEPOSITS OF S.W. MISSOURI. 249 



between the ore and the chert is sharp, and no ore is found in the 

 mass of the chert itself. The chert is hard and unaltered. The 

 galena is as coarsely crystalline in its structure as the respective 

 widths of the fissures would allow, showing that the ore has crys- 

 tallized out of a very thin solution, which must have filled the fis- 

 sures for a very long period without interruption. 



4. Irregular deposits of galena, in loose accumulations of 

 broken chert, arc very frequent, especially in the Joplin district. 

 The whole lower part of Joplin creek valley is filled with such 

 accumulations to a considerable depth, in places to more than 70 

 feet. The galena found in these loose chert masses is partly old, 

 partly of more recent formation. The former seems to have been 

 deposited, while the chert beds were simply fissured, but not 

 greatly disturbed from their position. Afterwards, when these 

 beds became gradually more and more broken through the trans- 

 formation and dissolution of the underlying limestones, the galena 

 seams broke down with the chert beds, and the quantity of ore 

 was increased by the addition of all that ore which may have 

 been originally contained in the limestone strata, now removed 

 by dissolution. The galena in these deposits is therefore in part 

 loose, in part adhering to chert fragments. It frequently shows 

 signs of friction and impressions of sharp-cornered chert frag- 

 ments. The crystals are often compressed, and loose pieces are 

 rounded off. But besides this galena, which was formed in the 

 original strata, in some localities intact and well developed galena 

 crvstals occur deposited on all sides of loose chert fragments. 

 This fact shows that the deposition of 1 his ore has continued dur- 

 ing the slow destruction of the strata, and that it has continued 

 after the chert was. as it now is, entirely broken up into loose 

 fragments. 



5. Seams and impregnations in quartzite represent the fifth and 

 last form of lead and zinc deposits observed in Southwest Mis- 

 souri. They occur in some localities near Joplin, but are espe- 

 cially represented in the mines of Oronogo (late Minersville). 

 There we find considerable masses of quartz rock, partly dis- 

 tinctly crystalline and composed of either pyramidal or prismatic 

 crystals, partly very line-grained or subcrystalline. This rock is 

 mostly of gray or of grayish-brown color. It is often impregnated 

 with bitumen, and emits a bituminous odor when broken. It 



