40 GEOLOGY OF ILLINOIS. 



Limestones for lime. The best and purest limestone for the manufacture of 

 quick lime, will be found in the Keokuk and Burlington limestones. The up- 

 per or concretionary member of the St. Louis group, which is generally pre- 

 ferred for this purpose, was not met with in this county, and if found at all, 

 would be too local in its development to supply any considerable portion of the 

 county, but the limestones above named, one or both of them, are easily acces- 

 sible at most points in the county, and when the rock is carefully selected, they 

 afford a very good material for this purpose. 



Hydraulic limestone. Some of the upper beds of the Kinderhook group, in 

 the vicinity of Mr. Churchill's place, just above the village of Kinderhook, 

 presents the usual appearance of a hydraulic limestone, and a specimen of the 

 rock analysed by the late Mr. Henry Pratten, gave the following results : 



Water 2.82 



Silica 7.00 



Alumina 0.77 



Carbonate of Lime 68.15 



Peroxide of iron 0.77 



Protoxide of manganese 2.11 



Carbonate of magnesia 18.55 



This analysis would seem to indicate too large a per cent, of carbonate of 

 lime, and too small a proportion of the silicates of alumina and iron, to form a 

 good cement rock, but further tests might show that the rock was well adapted 

 for this purpose. 



Clay and sand. The fire clay which usually underlies the coal, if tolerably 

 free from lime, is valuable for the manufacture of fire brick and common pot- 

 tery, and where the coal seams are thin, it can be mined with the coal to good 

 advantage. The brown clays of the Drift furnish an abundant material for the 

 manufacture of common brick, and sand is abundant in the valleys of the streams. 

 The Loess often affords these materials in just the right proportion for the use 

 of the brick machine. 



Marble. The bed of oolitic conglomerate, already mentioned as occurring 

 in the Kinderhook group at Rockport, receives a fine polish and makes a beau- 

 tiful variegated marble. The bed, however, is only about three or four feet in 

 thickness, and can not be easily worked where it outcrops in the bluffs, on ac- 

 count of the thickness of the beds which overlie it, but it may be found in 

 some of the lateral vallies in that vicinity, where it could be quarried at less 

 expense. Some of the sub-crystalline beds of the Burlington limestone receive 

 a high polish, and make a fine ornamental stone. 



Mineral Springs. Perry Springs are situated about two and a-half miles 

 southeast of the town of Perry, on a small branch of one of the tributaries of 

 McGee's creek. The springs, three in number, issue from the upper part of 

 the Keokuk limestone, which underlies the valley, and outcrops along the bluffs 



