236 2'he Aiuen'rdv (ieologisf. April, 1895 
Lower (JarVxinifcrous rocks are the Jiiost abuiulant. and in 
these the principal ore deposits are to be J'oiintl. In tlie east- 
ern portion of this district, however, there are a number of 
deposits in the Ozark rocks. The age of the rocks of tlie 
Ozark stage lias long l)eeii a mooted question. The^y were 
originally classed as the ecjuivalent of the Calciferous rocks 
of the New York section and recent investigation goes to 
prove the correctness of this view.* The rocks consist in the 
main of niagnesian limestf)nes of varying texture, with inter- 
calated beds of sandstone. Considerable chert is associated 
with them. The rocks of the Lower Carboniferous belong to 
what is generally known as the Burlington grouj), including, 
however, patches of Keokuk and rocks of the Ivinderhook 
group. The ore deposits, however, are confined i)riiicipall_y 
to the Burlington rocks. These consist mainly of fine, 
coarsely cr3'stallized limestones, associated in places with 
beds of light colored, brittle chert, which are sometimes lo- 
cally greatly (U'veloped, and occupy a large part of the 
section. 
Structurally, the geology is (juite simple. There is one 
master flexure expressed in the quaquaversal dip of the rocks 
from the Archean center. Beyond this there are a few minor 
flexures and also a few well marked faults. There are also a 
large number of minor faults and crevices unaccompanied by 
movement. 
In the southwestern district the ore deposits are found al- 
most wholly in the Lower Carljoniferous rocks. In the central 
and southeastern districts they are confined entirely to the 
Lower Silurian. The deposits of the southwest are largely of 
zinc ore, while in the southeast lead is the principal ore mined. 
The different distric^ts are characterized by special forms of 
deposits. Thus, in the southwest the usual type is the mas- 
sive. The ore body is frequently several hundred feet in 
diameter, consisting of f)re and gangiie and surrounded by a 
more or less barren limestone or chert bars. Stringers or 
sheets of ore may run out into the country rock, but these are 
not of sufficient size to affect the general form. In the east- 
ern part of this district, tabular deposits in vertical crevices 
■*For llic details of this iiivcstiiration. tlie i-cadci- is refprn-d to tlic Ri'- 
I);)rt (Ml L('n<l ami /inc. Mo. (WmiI. Snrv.. I'l. I. pp. :!7S-:iS."). 
