Paleozoic Rocks in the Mississippi Basin. — Keyes. 
109 
detached and the soft parts have left no trace, whereas the 
tougher skins of the cladodont sharks in the same strata have 
preserved for us not only the forms of the fishes but in several 
instances the contents of their stomachs, giving ample proof, 
if such proof had been necessary, of the nature of their pre} T . 
THICKNESS OF THE PALEOZOIC ROCKS IN THE 
MISSISSIPPI BASIN. 
By Charles R. Keyes. Jefferson City, Mo. 
The thickness of the Paleozoic strata of the central Missis- 
sippi basin has been variously estimated. With a single 
exception the calculations place the number somewhere be- 
tween 4,000 and 6,000 feet, or in the neighborhood of one mile. 
The figures obtained of late years have tended to reduce con- 
siderably the earlier estimates ; and the most recent informa- 
tion goes to show that even these are still somewhat excessive. 
The chief discrepancies in the various estimates are to be 
found in the Carboniferous and in that portion of the geolog- 
ical column below the Trenton, which is one of the best marked 
horizons in the region. There is close agreement regarding 
the vertical measurement of the median portion, the Devonian 
and the upper part of the Silurian. Tabulated the various 
figures are as follows : 
Below 
Date. 
Name. 
State. 
Total. 
Coal M. 
Trenton. 
1855 
Swallow- 
Missouri 
4,200 
600 
1,400 
1858 
Hall 
Iowa 
8,40(1 
1,000 
800 
1866 
Worthen 
Illinois 
4,300 
1,200 
300 
1872 
White 
Iowa 
3.800 
800 
70(1 
1893 
Keyes 
Iowa 
2,700 
1,600 
600 
1891 
Broadhead 
Missouri 
5,500 
2,000 
1,300 
1891 
Keyes 
Missouri 
4,100 
1,600 
7(i(» 
1895 j 
Norton 
Iowa 
3,500 
1895 | 
Keyes 
Missouri 
3,000 
Stratigraphically the territory west of the Mississippi, cov- 
ering an area somewhat larger, but approximately of the same 
shape as the Western Interior coal field, is a broad shallow 
basin. Its margin sweeps in a wide curve from west -central 
Minnesota to the southeastern part of that state, through 
southwestern Wisconsin, western Illinois, across central Mis- 
souri into Indian Territory. The center or lowest portion is 
probably not far from where the Iowa-Missouri boundary line 
intersects the Missouri river. The marginal roeke are chiefly 
