smith,] LEAD AND ZINC OP JOPLIN DISTRICT. 201 
extending from the town of Duenweg northwesterly between Webb 
City and Carterville to Oronogo. They reach their greatest develop- 
ment south and southeast of Carterville. The rocks in which the ore 
occurs are bedded cherts, horizontal or nearly so. The ore is found 
mainly along the bedding planes, though it also occurs in seams in 
the somewhat broken beds. Much of that occurring along the bedding 
planes is disseminated in a dark secondary chert which appears to 
fill cavities left by the removal through solution of limestone lenses. 
The ore is mainly sphalerite, with a minor proportion of galena, and 
a still smaller amount of marcasite. Deposits of this form are always 
near ore bodies belonging to the second class. 
The latter may be divided into (1) linear deposits (runs), (2) circu- 
lar or elliptical deposits, and (3) irregular deposits. The linear depos- 
its consist of comparatively narrow bodies of ore, either vertical or 
inclined, following a roughty uniform direction. The ore is as a rule 
mainly or wholly sphalerite; where it is associated with galena the 
latter occurs usually in the upper part of the deposit. The sphalerite 
is found both disseminated., for the most part in a dark secondary 
chert matrix or in selvage, and cementing chert breccia or lining 
interstices of the breccia or solution cavities in limestone or dolomite. 
It is often associated with calcite and pink dolomite. The rocks in 
which the ore occurs are generally brecciated cherts which have been 
recemented to a greater or less extent, either with black secondary 
chert or with calcite, sphalerite, dolomite, or galena, either separately 
or in combinations of two or more. In the vicinity of Joplin this brec- 
cia with its ore occurs almost without exception against a barren wall 
of chert and limestone, the latter altered to a coarse-grained gray 
dolomite, apparently closely connected with the deposition of the 
sphalerite. In these same deposits galena, where it occurs, is usually 
found tilling cracks in the fractured cherts, near the upper limits of 
the sphalerite and for the most part near its outer margin, i. e., away 
from the dolomite. 
The chert breccias in which the linear deposits occur are due largely, 
to faulting, though to a minor extent developed by folding. Breccias 
produced by folding may be associated with those resulting from 
faulting. The ores in the former occur, as a rule, along the flanks of 
the folds. Where two faults meeting at an angle have developed at 
the same time, the brecciation, with its accompanying deposit, formed 
along one fault, instead of crossing the other fault at the point of 
meeting, may take the direction of the intersecting fault, thus forming 
one continuous deposit; and the two faults, instead of meeting at an 
angle, may be joined by a curve. Such deposits are closely related 
in manner of formation to the deposits of the following type. 
Circular or elliptical deposits are a modification of the Linear deposit. 
A horizontal section of these ore bodies would have the form of a 
roughly circular or elliptical ring, inclosing a central barren "core." 
