158 CEMENT MATERIALS AND INDUSTRY. [bull. 243. 
usually not suitable in composition for cement manufacture. The 
Pella beds are more important. They outcrop widely and are, in 
composition, excellently adapted to cement manufacture. The}^ fringe 
the productive Coal Measures on the east and occur as scattered 
inliers within the general area of outcrop of the coal beds. This 
results from the pronounced unconformity between the Des Moines 
and the St. Louis, hills of the limestone rising like islands above the 
lowest coal beds. 
The Pella beds usually show an upper portion consisting of calcare- 
ous marl Avith some thin beds of limestone. This facies is ordinarily 
8 to 10 feet thick. Below it are beds of fine-grained blue to gray 
limestone, breaking with clean conchoidal fracture, and usually thin- 
bedded. The rock is very rarely magnesian, and the analysis quoted 
below is quite representative. The sample was taken from the Chil- 
ton quarry at Ottumwa by Mr. T. E. Savage. The beds exposed at 
this quarry are noted in the following section: 
Chilton quarry section. 
Feet. 
1. Fine-grained, dark-colored, pebbleless soil 1 
2. Clay, reddish brown, with pebbles 3 
3. Sandstone, brown, iron-stained, mostly incoherent, but in places indurated 
( Des Moines) J 10 
4. Calcareous shale, weathering into small bits, very fossiliferous 3 
5. Limestone, dense, fine-grained, gray 2£ 
6. Limestone, shaly, soft, weathering readily, similar to No. 4 2 
7. Limestone, dense, fine-grained, gray 1£ 
8. Shale, calcareous 3 
9. Limestone, hard, fine-grained, gray, fossiliferous 1 ^ 
10. Limestone, dense, bluish 1 
11. Limestone, dense, finer-grained, bluish gray, in part massive, in part thin- 
bedded, fossiliferous 4 
12. Limestone, hard, gray 1 J 
13. Limestone, dense, gray 1 h, 
COMPOSITION. 
An average sample of the limestone here was analyzed in the labo- 
ratory of the United States Geological Survey by George Steiger 
with the following results: 
Analyses of St. Louis limestone at Ottumwa. 
Silica (Si0 2 ) 6.83 
Alumina ( A1 2 3 ) " 2A2 
Iron oxide ( Fe 2 3 ) 54 
Lime ( CaO )..... 49. 54 
Magnesia (MgO) 07 
Sulphur trioxide (S0 3 ) 13 
a This figure includes any Ti0 2 or P 2 5 present. 
. 
