THE CHESTER SERIES IN ILLINOIS 407 



thicker than it is north of Big Muddy River. At one locality in 

 the bluffs northwest of Buncombe, in Johnson County, the lime- 

 stone is about one hundred and forty feet thick and in the entire 

 belt across the state the minimum thickness seems to be not less 

 than sixty or seventy feet. 



The fauna of the Kinkaid limestone, so far as it is known, is 

 not so prolific as is that of several of the older limestones in the 

 Chester series, but it resembles these earlier faunas in its general 

 characters, consisting, as it does, of the same genera of brachiopods 

 bryozoans, and blastoids. The pelecypod Sulcatopinna mis- 

 souriensis, which is so characteristic of the Menard, is also present 

 in the Kinkaid, and associated with it is the large form of Spirifer 

 increhescens . The specimens of Composita, however, which have 

 been met with in the Kinkaid, are of the smaller type, like those 

 in the Middle and Lower Chester limestones. A form that is very 

 common in the Kinkaid is a species of Martinia, a genus which is 

 commonly wanting in other Upper Chester faunas, and is only 

 locally common in the Middle and Lower Chester horizons. The 

 bryozoans have nowhere been found to be so abundant or so well 

 preserved in the Kinkaid as they ^.re in the earher Chester lime- 

 stones, but those that are present are members of the same genera 

 as are represented elsewhere, and most of the species are also 

 believed to be present in the lower horizons. 



GEOLOGICAL CROSS-SECTION 



The relations of the several Chester formations in Illinois 

 which have been described in the preceding pages are shown in 

 the accompanying diagrammatic section. This section is intended 

 to illustrate the sequence of beds from Hardin County at the 

 southeast to Randolph and Monroe counties at the northwest. 

 The sandstone units are shaded in the diagram, the limestone- 

 shale units being left blank. The diagram has been constructed 

 as if the upper units of the formational succession were continuous 

 to the extreme northwestern extension of the Chester beds in St. 

 Clair County. This is not the actual condition, however, for the 

 entire series of beds is truncated by the Pottsville, so that these 

 basal Pennsylvanian strata, in passing northward from Randolph 



