i ti The American Geologist. August, 1893 
It is in the limestones of this series that the lead, nickel, 
cobalt and copper of Mine La Motte and tin- St. Joe mines 
arefound. A few fossils arc also found as Lingulella lamborni 
Mk... in shales at Mine La Motte, and Lingula and Scolithus, 
near Fredericktowii. and Obolella polita near Polks. In Mad- 
ison count}' and elsewhere in southeast Missouri other fossil- 
were obtained from chert beds on the highest hills, whose 
position is probably either in the Second sandstone or just 
below. Other fossils were also found in residual masses of 
chert occupying a topographical position near the foot of the 
hills, but which are probably of the same geologic age as tin- 
other chert fossils. Among those fossils were observed Orthis, 
Orthoceras, Murchisonia, Maclurea, Capulus,Straparollu8, Lit- 
uites, Cyrtoceras, Ophileta. 
These lower limestones with the basal sandstone of Madison 
county may include over 300 feet, and seem evidently to be 
lower than the Third Magnesian limestone of central Missouri. 
The limestones may be the equivalent of Prof. Swallow's 
Fourth Magnesian. As. Prof. Swallow's Third sandstone has 
not been recognized in southeast Missouri it would be difficult 
to say where the Third ended and the Fourth begun. We may 
say Lower Magnesian or Third Magnesian. They are cav- 
ernous and many fire springs of water issue from them. They 
are the basal members of the Ozark series. 
The Thihd Magnesian limestone is easily recognized by its 
peculiar subvitreous appearance. It is generally coarse 
grained, light colored and slightly bluish gray or flesh-colored, 
often cavernous, sometimes forming natural bridges. Most of 
the caves of southern Missouri occur in this formation and 
some of them are very handsome with numerous stalactites 
and onyx deposits. In Washington count} 7 it incloses numer- 
ous mammillary crystallizations of quartz, which seem to be 
secondary deposits in small cavities in the limestone. It is 
lead-bearing in southeast and central Missouri, the ore-bear- 
ing beds being chiefly within the Ozarks, and generally 30 to 
4(1 miles from their margin. The limestone at the mines is 
often found decomposed. The lower Magnesian limestones, 
including the Third and Fourth, often occur in thick beds, 
as on the Niangua, Osage and St. Francois and their tribu- 
taries. 
