THE CHESTER SERIES IN ILLINOIS 



STUART WELLER 



University of Chicago 



PART II 



UPPER CHESTER GROUP 



Tar springs sandstone. — Like the Lower and Middle Chester 

 groups the Upper Chester is initiated by an important sandstone 

 formation which is named the Tar Springs. This name was 

 first used by Owen many years ago for a sandstone in Breckin- 

 ridge County, Kentucky, and has been revived by Butts^ at a 

 recent date. This sandstone is a persistent formation across 

 Hardin, Pope, and Johnson counties, as far as the detailed mapping 

 has been carried, and it doubtless continues into Union County. 

 The sandstone is variable in character. In some places in the 

 area which it occupies it is as massive and as conspicuous a cliff 

 maker as the Cypress; this is especially true in some portions of 

 Hardin County. Elsewhere it is nearly all thin-bedded. Much 

 of the sandstone is conspicuously cross-bedded. Throughout 

 much and perhaps the whole of the Chester belt across the southern 

 counties, the Tar Springs sandstone is divided into an upper and 

 lower member by a persistent shale bed, which has associated with 

 it in widely separated localities a thin layer of impure coal, in 

 some places only an inch or two in thickness but elsewhere a foot 

 or more. The more massive layers of the sandstone resemble the 

 Cypress and Hardinsburg in color and texture, but in much of 

 Pope and Johnson counties, where the formation is more thinly 

 bedded, it is distinctly darker brown than any of the older Chester 

 sandstones. 



The thickness of the Tar Springs sandstone varies considerably. 

 In Hardin County it is one hundred feet or more thick, perhaps 

 as much as one hundred and fifty feet locally, but it diminishes to 



' Mississippian Formations of Western Kentucky (191 7), p. 103. 



395 



