198 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
& 
the smaller streams are determined bylines of shale deposits, alon 
zones of faulting and consequently lines of weakness. As the shales 
are the softest rocks of the region, there is thus a double reason for 
the correspondence of the valleys with these lines, and probably the 
same facts explain the general limitation of mining to the valleys and 
their slopes. 
GEOLOGY. 
Stratigraphy. — The geology of the district is simple. The rocks 
are wholly sedimentary, and those exposed on the surface are all of 
Carboniferous age, both Upper and Lower Carboniferous being repre- 
sented. The Lower Carboniferous rocks consist of about 350 feet of 
cherts and limestones in varying proportions. This is the ore-bearing 
formation of the district, the ore occurring especially in the more 
cherty portions. The limestone is generally nonmagnesian, but a 
comparatively small amount of dolomite occurs, mainly as the result 
of alteration of the limestone at the time of the deposition of the ores. 
The limestone generally contains a considerable amount of organic 
matter, evidenced by I lie vaseline-like odor which is characteristic of 
the rock when broken; and occurrences of bitumen are common, 
especially in association with the mineral deposits. Not far from the 
top of the series is a thin but persistent bed of oolite, outcrops of 
which occur over the entire district. Some distance below is a heavj^ 
bed of chert, about 50 feet thick, known as the Grand Falls chert. 
The Lower Carboniferous rocks are exposed over the greater part 
of the Joplin district. Above them, when not eroded, lie the Upper 
Carboniferous Coal Measure shales and sandstones. The shales, 
which constitute the greater part of the Coal Measure expos ures of 
the quadrangle, are frequently associated with thin beds of coal. 
The sandstone occurring with these shales is sometimes changed to 
a quartzite through the infiltration of secondary silica. There is a 
considerable area of these shales and sandstones in the northwest 
corner of the quadrangle, in addition to small patches of shale over the 
entire district. These smaller occurrences in some cases represent 
outlying hills left on the removal of the Coal Measure rocks; in other 
cases their persistence is due to their occurrence in pre-Coal Measure 
erosion basins, or in later basins formed by the folding of the rocks, 
while in still others they are the result of faulting. 
Beneath the Lower Carboniferous limestones and cherts is the 
Devono-Carboniferous shale. The occurrence of. this formation in 
the Joplin district has not been proved, though it is believed to be 
present as a thin bed of shaly limestone having an average thickness 
of only a few feet. The Cambro-Silurian rocks beneath the Devono- 
Carboniferous shale consist of a series of magnesian limestones, 
dolomites, and sandstones. As none of the rocks below the Lower 
Carboniferous are exposed in this district, their occurrence can be 
determined only from deep borings. 
