160 Geology of Upper Iilinois. 
Clays, well suited to brick making, are abundant in the prairie 
country ; and others, adapted to the manufacture of fire brick and 
pottery, are found overlying the horizontal coal near Ottawa, and 
at the mouth of the Kankakee. 
Extensive beds of pure, white sand, derived from the decom- 
position of the sandstone, occur north of Rockwell, near the little 
Vermilion. It is advantageously employed in the fabrication of 
mortar and plaster, and will one day lead to the production of the 
finer qualities of glass.* 
The extraordinary crops of grain and potatoes every where ob- 
tained from the prairie lands, induced me to submit’a portion of 
the soil to chemical analysis. 'The sample was taken from eight 
inches below the surface, and after being thoroughly dried by 
several weeks’ exposure to the air, it afforded the following result 
on one hundred parts. 
Water of absorption, - - . . 8.50 
Organic matter, - - . - 9.50 
Silica, - - - - - 70.00 
Saeco. Se ae mot 
Carbonate of lime, - --. - -- &# 1.50 
Carbonate of magnesia, 
Sulphate of potash, ; 
In depth and fertility of soil, the Illinois prairies are probably 
unsurpassed by any tract of country in the known world. Fields 
near Alton have been planted with Indian corn for fourteen years 
in succession, without the addition of manure, and still continue 
to yield an abundant crop. The farmer in this region, moreover, 
enjoys a great advantage in the boundless extent of cleared land 
within his reach, which permits him on the exhaustion of tracts 
long under tillage, to bring into cultivation fresh fields, and thus 
to allow those which are exhausted to recover their strength, by 
enjoying a fallow. Occasionally also, where the soil is light, as 
on the Illinois bottoms, near Buffalo rock, gypseous marls, like 
mei ee ef 
* A variety of limestone occurs adjoining the canal, a little east of Camp-rock, 
well suited to the fabrication of water-cement. The precise locality may be learned 
on application to Mr. Dixwext Larurop, of Rockwell, a gentleman whose pub- 
ee and intelligence render him of essential service to the region in which he 
