260 GEOLOGY OF ILLINOIS. 



In the foregoing section the beds numbered from 2 to 18 inclusive be- 

 long to the Coal Measures, and include the two lower coals. No. 19 is 

 undoubtedly the St. Louis limestone which outcrops on Spoon river just 

 below Seaville, about eight miles east of Prairie City. At Lawrence's 

 mound, at an elevation considerably above the surface where the above 

 boring was made, a coal seam three feet in thickness was found in dig- 

 ging a well, which was probably No. 3, occurring here as an outlier left 

 by the denuding forces which swept it away from the surrounding region. 

 It lay immediately below the drift, with no roof but gravel, and covered 

 but a limited area of ground. 



At Macomb, a boring, carried to the depth of about 160 feet, tailed to 

 find any coal of sufficient thickness to be of any economical value. From 

 these experiments it would seem that the lower coals in this county are 

 not very uniform in their development, and probably neither No. 1 nor 

 No. 3 will be found over any considerable area thick enough to be 

 worked to advantage, while No. 2 is also too thin to be worked at some 

 points, though it may be considered the most persistent and reliable 

 seam to be found in this county. 



St. Louis Limestone. This division of the Lower Carboniferous series 

 is probably nowhere in this county more than fifty feet in thickness, and 

 consists first, of a bed of light-gray concretionary or brecciated lime- 

 stone, laying immediately below the lower sandstone of the Coal Mea- 

 sures j and secondly, of a. magnesian limestone and some blue shales or 

 calcareous sandstones, constituting what is sometimes called the "War- 

 saw limestones." On the east fork of Crooked creek, a little north of 

 west from Colchester, the following section of these limestones may be 

 seen : 



No. 1. Brecciated light-gray limestone 5 to 20 feet. 



No. 2. Calcareous sandstone in regular beds 12 " 



No. 3. Bluish shale 3 " 



The magnesian bed, which usually forms the base of this group, is 

 below the surface here, and generally ranges from eight to ten feet in 

 thickness. The brecciated limestone is very unevenly developed, and 

 often varies in thickness in a short distance from five to twenty feet or 

 more. It rarely affords any fossils except the common corals Litltostro- 

 tion canadense and L. proliferum, silicious specimens of which are often 

 found weathered out along the creeks where this limestone outcrops. 

 No fossils were seen in the calcareous sandstone, but the inaguesian 

 limestone that outcrops lower down on the creek, and underlies the blue 

 shale in the above section, usually contains a variety of Bryozoans, 

 among which are the Archimides Wortheni, Polypora Varsoviense, Semi- 

 coscinium Keyserlingi, etc. 



