160 Geology of Upper Illinois. 



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 aflforded the following result 

 on one hundred parts. 



Water of absorption, - - - - 8.50 



Organic matter, - - - - 9.50 



Silica, - - - - - - 70.00 



Alumina, - - - - - - 7.50 



Carbonate of lime, - - - - 1.50 



Per-oxide of iron, - - - - 1.00 



Carbonate of magnesia, > 



„ - , - ° ' > - - - traces. 



feulphate 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 



* 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. Dixwell Lathrop, of Rockwell, a gentleman whose pub- 

 lic spirit and intelligence render him of essential service to the region in which he 

 resides. 



