330 
CEMENT MATERIALS AND INDUSTRY. 
[bull. 24 
„ 
entirely of thia rock. The fact that it does not occur in thicker beds prevents it 
universal use as a building stone. Very frequently this glass rock is packed full o 
fossils. It is a- comparatively pure limestone, containing only a small amount o; 
magnesia, the chief impurities being silica and clay. 
The composition of this rock is shown by the following analyses, j 
Analyses of Platteville limestones, Wisconsin. 
z 
Silica (SiO,) 
Alumina (A1 2 3 ) 
Iron oxide (Fe 2 3 ) 
Lime carbonate (CaC0 3 ) . . 
Magnesium carbonate (MgCO s ) 
Water 
1 
2 
1 
r 6.16 
[ 1.10 
| 2.26 
1 
[ 1.90 
97.92 
85. 54 
1.60 
3.98 
n. (1. 
.93 
7.0J 
2.21 
1.25 
S4.05 
5. 3i 
.61 
1. Near Benton, on the Fever River, Geol. Wisconsin, vol. 2, pp. 560-561. 
2. Mineral Point, Geol. Wisconsin, vol. 2, pp. 560-561. 
3. Bristol, Dane County, Geol. Wisconsin, vol. 2, pp. 560-561. 
QUATERNARY SHELL MARLS. 
As in Michigan, Ohio, New York, and other States north of the- 
glacial limits, many lakes occur in Wisconsin, and some of these con<i| 
tain deposits of marl. Little attention has yet been paid to thesf* 
marl deposits and practicall} T nothing can be said as to their occurrence i 
and character. One noteworthy feature, however, should be born&i 
in mind. As already shown, almost all of the limestone deposits o\\ 
the State are highly magnesian. As the marls are ultimately derived 
from local limestones, it is to be expected that Wisconsin marls wil 
carry larger percentages of magnesia than marls occurring in areas OS J 
pure limestones. This seems to be indicated by the following analysis 
Analysis of shell marl, Wisconsin. 
Silica ( Si0 2 ) 1.4* 
Alumina ( A1 2 3 ) \ 
Iron oxide (F 2 3 ) J 
Lime carbonate (CaC0 3 ) i 86. 01 I 
Magnesium carbonate (MgC0 3 ) 7. 1* 
Sulphur trioxide (S0 3 ) M 
Water 1. ffi 
Organic matter 951 if 
Sections 17, 18, 19, and 20; town of Pierce, T. 24, R. 25. Kewaunee County. G. Bode, analyst 
Geology of Wisconsin, vol. 2, p. 239. 
