200 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
ORE DEPOSITS. 
Minerals. — The principal minerals of the Joplin district are sphal- 
erite (locally called "jack"), galena ("lead"), calcite ("tiff"), dolomite 
("spar"), marcasite and pyrite, mainly the former (both called "mnn- 
dic"), chalcopyrite ("copper"), cerussite and anglesite (both known 
as "drjr-bone"), calamine ("silicate"), and smithsonite. Calamine 
and smithsonite have generally been confused in this district, and 
most of the smithsonite, which in reality occurs more frequently than 
has been heretofore supposed, has been mined as "silicate." 
Distribution of ores and minerals. — Of the lead and zinc ores the 
sulphides, sphalerite and galena, occur for the most part below the 
level of underground water; the sulphate and carbonate of lead and 
the carbonate and silicate of zinc, being all oxidation products of the 
sulphide ores, occur mainly above that level, together with the more 
or less oxidized gangue and country rock. The deposits below ground- 
water level represent the concentrated ores, both those of first con- 
centration and those of secondary enrichment. They are frequently 
associated with more or less marcasite or pyrite, though these are as a 
rule inconsiderable in amount. In these deposits the galena is usually 
found at the upper levels (except in sheet ground, described here- 
after) tilling fractures in broken or brecciated cherts, and usually 
associated with more or less sphalerite. Only sphalerite (frequently 
with some iron sulphide) is found at the lower levels. It occurs (1) 
as a cement in chert breccia; and (2) disseminated in a black, second- 
ary chert which cements the brecciated cherts and also occurs in 
lenticular bodies along the bedding planes in sheet ground. Sphaler- 
ite is also found in small quantities disseminated in shale, in selvage, 
in mud, in limestone, or in dolomite. 
To sum up, the vertical distribution of the ores shows: 
First. Above underground water level, galena and occasionally 
some sphalerite; also the oxidation products, the carbonate and sul- 
phate of le ; ad and the carbonate and silicate of zinc. 
Second. Below underground water level, the sulphide zone. Some- 
times, but not always, galena dominates in the upper part of this 
zone, with sphalerite dominant in the lower and greater part of the 
zone. This succession does not always hold, and some mines have 
yielded mainly galena throughout, while mines yielding sphalerite 
with little or no galena are common. In the typical sheet ground 
galena and sphalerite usually occur together and associated with 
marcasite. 
Forms of ore deposits. — In considering the forms assumed by the ore 
deposits, the ore bodies in the mines of this district may be roughly 
divided into two classes, (1) horizontal or nearly horizontal deposits; 
and (2) vertical or inclined deposits. The first class includes the 
tabular bodies of ore known as blanket veins or sheet ground. Depos- 
its belonging to this class are mainly limited in occurrence to a belt 
