152 CEMENT MATERIALS AND INDUSTRY. [bull. 248. I 
includes near Rock Island a very pure limestone, as is shown by the 
following analysis: 
Analysis of Fayette breccia.® 
Insoluble 0. 42 J 
Iron (as carbonate) 36 1 
Lime carbonate (CaC0 3 ) 98. 77 j 
Loss, alkalies, etc 45 
Samples of the Otis and Kenwood beds from a railway cut 2 miles 
north of Cedar Rapids showed so much magnesia as to preclude the 
use of the rock. 
CEDAR VALLEY LIMESTONE. 
DISTRIBUTION. 
The most important member of the Devonian of Iowa, as measured 
either by areal extent or thickness, is the Cedar Valley limestone. It 
extends from Muscatine County on the Mississippi to the Minnesota 
line in a broad belt trending northwest. It has an estimated maximum 
thickness of 300 feet and rests to the southeast on the Wapsipinnicon 
formation. To the northeast it comes by overlap to rest on the 
Maquoketa shale. 5 To the southwest it is in turn covered by rocks of 
the Mississippian series, while on the northwest the Lime Creek shales 
intervene between the latter and the Cedar Valley. 
COMPOSITION. 
In the southern portion of the area of outcrop the Cedar Valley 
limestone is characteristically a nonmagnesian limestone, which is usu- 
ally fine grained and breaks with a sharp conchoidal fracture. This 
phase of the formation is excellently exposed in Johnson County, and 
the following analysis was made by George Steiger, in the laboratory 
of the United States Geological Survey, from an average sample rep- 
resenting the rock quarried at Iowa City. These quarries exposed a 
total thickness of about 50 feet. 
Analysis of Devonian limestone at hum, City. 
Silica (Si0 2 ) 3. 08 
Alumina (A1 2 3 ) - c .l- 24 
Iron oxide (Fe 2 3 ) 73 
Lime (CaO) 50. 30 
Magnesia (MgO) 2. 22 
Sulphur trioxide (S0 3 ) 06 
Toward the north the limestone becomes more magnesian, until in 
Howard Countv it is a massive dolomite which has been mistaken for 
a Hall, Geology of Iowa, p. 372. 
&Calvin, S., Geology of Howard County: Iowa Geol. Survey, vol 13, pp. 49-62. 
<• With the AU>, ; is included any Ti0 2 or P 2 5 present. 
