ECKEL.] IOWA. 157 
upper portion especially, is associated with abundant argillaceous 
shale, and often outcrops in steep bluffs, at the foot of which the shales 
of the Kinderhook are available. The beds are best exposed in Lee 
and Des Moines counties, but occupy portions of Louisa, Washington, 
Henry, and other counties in the southeast part of the State. 
At Burlington, in the south bank of Cascade Hollow, the following 
section was measured by Mr. T. E. Savage. 
< 'ascade Hollow section. 
Feet. 
1. Fine-grained, homogeneous soil material without pebbles, dark-colored 
al )« >ve, grading down to yellow below 4 
2. Clay with pebbles and small bowlders of granite and greenstone, reddish 
brown 6 
3. Limestone, much decayed, in layers one 1 to 4 inches thick, numerous 
chert nodules 5 
4. ( !hert f 
5. Limestone, crinoidal, coarse-grained, layers 4 to 8 inches thick 4 
6. Limestone, crinoidal, with chert nodules 1 
7. Limestone, coarse, crinoidal; at places massive, at others weathering into 
layers 3 inches to 1 foot thick, containing numerous fossils 10 
COMPOSITION. 
An average sample of this limestone was analyzed by George 
Steiger in the laboratory of the United States Geological Survey with 
the following results: 
Analysis of Burlington limestone. 
Silica (Si0 2 ) 5. 18 
Alumina (A1 2 3 )« \ 87 
I Iron oxide (Fe 2 3 )/~ " 
Lime (CaO) 52. 16 
Magnesia (MgO) 40 
Sulphur trioxide (S0 3 ) 00 
The beds outcropping at this point are thoroughly representative 
of the limestone of this formation. Greater thicknesses are exposed 
at other points, and the total thickness has been estimated to be about 
250 feet. 
ST. LOUIS LIMESTONE. 
DISTRIBUTION. 
The St. Louis is one of the most widely distributed formations in 
Iowa. It rests on the Osage and lies unconformably below the Des 
Moines formation. On account of its relation to the coal beds it has 
been carefully mapped and extensivel} T studied. It includes three 
i minor divisions, the Pella, the Verdi, and the Springvale beds. The 
Verdi and Springvale beds have limited areas of outcrop and are 
a This figure includes any Ti0 8 or P. 2 Os present. 
