llie M issourl Lead ami Zinc Deposits. — Robertson. 237 
occur more frequently, although massive or cavern deposits 
are also found. 
In the southeastern district we also have massive deposits, 
but the structure of the ore body is totally dissimilar to those 
just referred to. These consist of great masses of magnesian 
limestone in which the lead ore is disseminated in grains of 
varying size. As in the southwest, so in this district are 
found the tabular or sheet deposits, as well as lenticular and 
pipe deposits and stockwerke. These occur mainly in Jeffer- 
son, Washington and Franklin counties. 
The ore body is composed of a mixture of gangue, ores and 
accessory minerals. The gangues consist (jf countr}- rock, 
clays, sands and shales, secondary cherts and limestones, dol- 
omite and barite. 
The country rock is generally limestone, either pure or dol- 
omitic, or chert. It occurs both massive and fragmental. The 
former is seen in the southeastern district, where the ore is 
disseminated through large bodies of massive magnesian lime- 
stone. In the southwest, the country rock is mainly frag- 
mental and consists largely of chert breccia, although frag- 
ments of Coal Measure sandstone, shale and coal are met with 
in this breccia. The chert is angular, sometimes pitted, and 
while some blende or galena may occur in the crevices or cavi- 
ties, these minerals are never found in any quantity through 
the rock. In the southeastern district, where the deposit oc- 
curs in portions of the Lower Silurian rocks close to the 
Archean floor, water-worn boulders of granite are met with, 
(.'lays of many varieties are found in these dei)Osits. They 
are generally dark red in color, but also occur in all tints of 
red and yellow to pure white. Some of these lighter colored 
varieties are called "tallow clays," from their resemblance to 
tallow, and often contain a notable quantity of zinc. Sands 
resulting from the decomposition of cherts and (juartzite oc- 
<-ur in Jasper county and the adjoining Cherokee county, 
Kas. The shales consist of earthy sands and plastic and non- 
plastic clays which grade into sands on the one side and clavs 
on the otiier. They are sometimes [wirtly (•()nstili(h(ted and 
sometimes soft and of the c(»nsistency of miul. Secondary 
cherts consisting mainly of an amorphous chalcedonic silica 
are abundant as gangues in Jasper and Newton counties antl 
