296 GEOLOGY OF ILLINOIS. 



ceous, with much chert. This is the most northerly outcrop of the group in 

 this county, and in Henderson county it is exposed but a very little further 

 north. Thin outliers may be found for some distance in this direction, beneath 

 the Coal Measures, but, like the other members of the Sub-carboniferous serieSj 

 it soon thins out. 



In section 1, township 11, range 3, there are extensive quarries in this 

 limestone. Some of the layers are very light colored and even textured, and 

 are reported to take a good polish. Other layers, though not as light colored, 

 furnish a durable building material. Much lime is burned here, and the rock 

 being nearly a pure carbonate of lime, affords a good article. In section 2 and 

 the northwest quarter of 11, there are small outcrops. In sections 4, 5, and 

 the north part of 8, there are exposures all along sonic small streams. The one 

 in section 4 gave the following succession of strata : 



FEET. IN. 



1. Chert 2 



2. Thin bedded sandstone, with a little chert 7 



3. Limestone and chert 1 9 



4. Limestone 9 6 



5. Slope to the water, with outcrop of limestone , 5 6 



Much material, both for building and making lime, has been taken from 

 these places. As we go south, from the north line of the township, we find 

 thin outliers of the Coal Measures forming the tops of the bluffs, till in section 

 8 the Burlington beds disappear beneath the sandstone and conglomerate which 

 form the base of the Coal Measures. 



On Cedar creek, from Rockwell's mill in township 12, range 3, to Olmstead's 

 mill in township 11, range 2, this limestone outcrops almost continuously along 

 the bluffs, frequently in perpendicular or overhanging ledges. Occasionally it 

 is covered by the sloping talus of the hills, but only to be again exposed a lit- 

 tle further on. In section 7 of the latter township, it is overlaid by a few feet 

 of the Coal Measures, and at this point gave the following section : 



FEET. IN. 



1. Slope, with outcrops of Coal Measure strata. Not measured. 



2. Slope, with outcrops of Burlington limestone 7 6 



3. Limestone and chert 3 2 



4. Compact calcareous clay shale 2 



5. Limestone 11 6 



6. Sandstone and limestone, to the bed of the creek 8 6 



Near the middle of section 7, on Cedar creek, and along a little branch put. 

 ting in from the southeast, there are extensive quarries in the bluffs, which 

 supply Monmouth and the adjoining region with large quantities of excellent 

 building material. As we proceed up the creek, the outcrops, though still 

 large, are not as extensive as below, being more frequently covered by the talus 



