TKEL.] ILLINOIS. 133 
Analyses of Trenton limestone from Thebes, Alexander County, 111.® 
[H. Pratton, analyst.] 
ica (Si0 2 ) 0. 06 
Lumina (A1 2 3 ) 
9A 
•on oxide (Fe 2 3 ) • J ' 
me carbonate (CaC0 3 ) 98. 01 
agnesinm carbonate (MgC0 3 ) 1 . 59 
ater 1. 07 
MISSISSIPPI A N LIMESTONES. 
DISTRIBUTION. 
The Mississippian limestones occur only in one belt, which extends 
irough western and southern Illinois. The northern end of this belt 
near New Boston, in Mercer County. From this point the limestones 
^tend southward along Mississippi River, in a belt averaging, per- 
ips, 20 miles in width, through Henderson, Hancock, Adams, and 
ike counties. A narrow branch of this belt extends up Illinois 
iver as far as Beardstown, and narrower bands border several of 
le larger tributaries of the Illinois. The main belt continues south- 
ard, parallel to and usually bordering Mississippi River, and covers 
ic greater part of Scott, Greene, and Jersey counties. Near Alton 
le limestone belt contracts until it is only a few miles in width, but 
idens out again a few miles south of Alton, and covers extensive 
•eas in Madison, St. Clair, Monroe, Randolph, and Jackson counties, 
ear the southern boundary of Jackson County the belt leaves the 
Ussissippi and turns eastward through Union, Johnson, Pope, and 
ardin counties. 
COMPOSITION. 
As in other States, the Mississippian limestones of Illinois are in 
eneral rather well adapted for use as Portland-cement materials, 
'ccasionally they contain beds carrying too much magnesium carbon- 
be for this use, but the commonest type is a limestone containing say 
[) to 95 per cent of lime carbonate, 1 to 4 per cent magnesium car- 
onate, and 1 to 6 per cent of silica, alumina, and iron oxide. The 
lalyses given below are therefore fairly representative of the 
lississippian limestones of Illinois. 
aGeology of Illinois, vol. 1, p. 148. 
