132 CEMENT MATERIALS AND INDUSTRY. [bull. l>43 
PORTLAND-CEMENT RESOURCES OF ILLINOIS. 
PORTLAND-CEMENT MATERIALS. 
Low magnesia limestones, suitable for use in Portland-cement man 
ufacture, occur in Illinois in three different geologic groups. The 
limestones of these groups will be discussed in the following order 
(1) Trenton limestones, (2) Mississippian limestones, (3) Coal Measure; | 
limestones. 
Of the three groups named above only one, the Coal Measures, ha 
yet been utilized in Illinois as a source of Portland-cement material 
though the Mississippian limestones, when their location, thickness n 
and composition are considered, would seem to be the most promisiiJ] 
group of the three. The Trenton group occurs in large areas, bin 
only a small part of the limestones usually included in it are sufficiently 
low in magnesia to be worth considering. 
TRENTON LIMESTONE. 
DISTRIBUTION. 
Though the so-called Trenton limestone covers a very large part o 
northern Illinois, it seems, in this part of the State, to be almos 
entirely a high-magnesia rock, and therefore unavailable as a sourc 
of Portland-cement material. In western and southwestern Illinois 
however, along the bank of Mississippi River, a number of isolate 
areas of Trenton limestone occur, and the rock from these localities 
to judge from the analyses available, is sufficiently low in magnesia t 
be used in Portland-cement manufacture. 
The geologic map (PI. IX, p. 220) shows the location of four sej 
arate areas of Trenton limestone in the district considered The firs> 
of these areas occurs on the east bank of Mississippi River at am 
below Thebes for a mile or two. The second area, larger than this I), 
extends along the east bank of Mississippi River from Harrison v ill 
to Smiths Landing, in the northern part of Monroe County. A this 
area is exposed along both banks of Illinois River, near Hartford, i 
Jersey County. The fourth area shown on the map occurs along th 
east bank of Mississippi River, south of Harding, in Calhoun County 
COMPOSITION. 
The only available analysis of Trenton limestone from any of thes 
areas in southwestern Illinois is that given below. It shows a ver 
pure nonmagnesian limestone. Similar occurrences of nonmagnesia 
limestones in the Trenton series across the river in Missouri will I 
found discussed on page 221, where further analyses are given. 
