DETAILS OF STRATIGRAPHY 369 



While the correspondence of the respective species of fossils compared 

 from the two areas is not identical, yet the differences between many of 

 them are slight. The fauna of the Channahon limestone is more closely 

 related to that of the Edgewood formation than to any other known 

 fauna. 



It is thought that the strata in the two areas represent about the same 

 period of deposition, and that the differences in the fossils are largely due 

 to local differences in the marine environments of the faunas in the re- 

 spective regions. 



THE ESSEX LIMESTONE 



Occurrence and relation to other strata. — The Essex limestone includes 

 the strata outcropping along Horse Creek, iy 2 miles east of the town of 

 Essex, in Kankakee County, Illinois. It occupies a position above the 

 Edgewood limestone and below the Sexton Creek (Brassfield) limestone. 



Detailed section. — The character of the Essex limestone is shown in the 

 following detailed section : 



Section of Essex Limestone near Essex, Illinois * 



Feet 



3. Sexton Creek (Brassfield) limestone : Yellowish-brown, much weathered 

 masses of magnesian limestone containing nodules and masses of 



chert bearing Pentamerella ? manniensis and other fossils Sy 2 



1,2. Essex limestone. 



2. Yellowish-brown, thin bedded, magnesian limestone, in layers 3> to 5 



inches thick, with numerous fossils 8% 



1. Rather hard, bluish colored, shaly limestone, in layers 2 to 6 inches 

 thick, exposed above the level of low water 2 



The contact between the members 2 and 3 in the above section is not so 

 clearly exposed that the presence or absence of a depositional hiatus be- 

 tween them could be certainly determined. Farther south, in Pike 

 County, Missouri, and Calhoun County, Illinois, Pentamerella ? manni- 

 ensis is a guide to the basal layers of the Sexton Creek (Brassfield) lime- 

 stone. Hence the upper limestone, number 3 of the section, is referred to 

 the Sexton Creek formation. The fauna of the Essex limestone, num- 

 bers 1 and 2 of the section, has not been recognized farther south in Illi- 

 nois and Missouri, where this limestone has probably been cut out by pre- 

 Brassfield erosion. The species arc listed below : 



Fossils from the Essex Limestone" 1 



Favosites cf. niagarensis Hall Bhynchotreta thel)esensis Foerste 



Halysites catenulatus Linn .sv// uchertella sp. 



Zaphrentis sp. Schucherteila cf. subplana (Conrad) 



25 The species of fossils from (lie IOssex and (lie Sexton Creek limestones will be figured 



and described in a later paper dealing with the stratigraphy and paleontology oi" these 



formations, now in preparation. 



