8 Geological History of the Ozark Uplift—Broad head. 
recognized over 200 feet of Magnesian limestone below the 
Third, and containing Lingulella lamborni Mk. From this 
occurrence I have referred these lower beds to the Potsdam 
group including also 20 feet of Ozark marble at the base, rest¬ 
ing on a few feet to 90 feet of sandstone and conglomerate. The 
latter reposes on the Archaean rocks, granites and porphyries. 
The latter prevail in Iron, Madison and St. Francois counties, 
with occasional peaks in Reynolds, Washington and Wayne. 
The granite occupies the lower hills and valleys, the porphyry 
rises into peaks a few hundred feet high to nearty 700 feet above 
the valleys. The evidence is that the sandstones and magnesian 
limestones (Potsdam and Calciferous) were deposited in Arch¬ 
aean valleys of erosion, for they generally repose nearly horizon¬ 
tally, or with slight inclination, upon the Archaean. 
The only exception is, that the Ozark marble beds are not 
always horizontal. The following section of rocks was taken 
by Dr. Shumard in Ste. Genevieve, and will serve to show what 
strata occur along the eastern margin: 
Lower Carboniferous..800 feet. 
Chouteau group.120 “ 
Devonian. 50 “ 
Upper Silurian.250 “ 
Hudson River group. 160 “ 
Trenton group. 250, “ 
First Magnesian limestone.150 “ 
First sandstone. 80 “ 
Second Magnesian limestone.250 “ 
Second sandstone.150 “ 
Third Magnesian limestone.200 “ 
On the northern side of the Missouri river we find that the 
Second Magnesian limestone is the lowest rock, near the west¬ 
ern line of St. Charles count}^, and continues to be so as far as 
ten miles west of Jefferson City. The Upper Silurian is not 
recognized along the same line, and the Devonian does not ex¬ 
ceed 100 feet in thickness, and thins out in the eastern part of 
Boone county. The Trenton thins out in the eastern part of 
Callaway county; and as we go west and south-west the Mag¬ 
nesian limestone series of the Calciferous is only separated from 
the Coal Measures by the Lower Carboniferous. 
The Magnesian limestone series are the rocks seen along the 
streams and on the hills throughout the Ozarks, generally the 
