100 ILLINOIS ACADEMY OF SCIENCE. 



THE ESSEX LIMESTONE. 



The strata comprising the Essex Hmestone overlie the Maquo- 

 keta shale in an exposure along the north bank of Horse creek, 

 about one and one-half miles east of the town of Essex, in Kan- 

 kakee County. Plate VII. shows the character of the rocks at 

 this place, and a detailed section of the strata is given below : 



Sections of Rocks Outcropping Along Horse Creek. 



Feet 

 3. Yellowish-brown, magnesian limestone, containing small nodules 

 and masses of chert, and bearing Pentamerella ? manniensis and 



other fossils 1}4 



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



inches thick, with numerous fossils 8J4 



1. Rather hard, bluish colored, barren shale, in layers 2 to 6 inches 



thick, exposed above the level of low water 2 



The lowest member of the foregoing section represents the 



Maquoketa shale. This shale is better exposed a few rods fur- 

 ther down the stream, where a thickness of eleven feet may be 

 seen, with no trace of the overlying limestone. The dolomitic 

 limestone, comprising the second and third members of the sec- 

 tion, constitutes the Essex limestone and contains the following 

 fossils : 



Fossils from the Essex limestone. 



Zaphrentis sp. 



Favosites cf. niagarensis Hall. 



Halysites catentilatus Linn. 



Atrypa marginalis (Dalman). 



Atrypa putilla (Hall and Clarke). 



Atrypa sp. 



Camarotoechia near acinus Hall. 



Camarotoechia? cUftonensis Foerste. 



Dalmanella elegantula var. 



Gypidula sp. 



Leptaena rhoniboidalis (Wilckens). 



Pentamerallaf manniensis Foerste. 



Rhipidomella hybrida (Sowerby). 



Rhynchotreta simplex Foerste. 



Rhynchotreta thebesensis Foerste. 



Schuchertella sp. 



Schuchertella subplana (Conrad). 



Strophonella sp. 



WhitHeldella cylitidrica Hall. 



WhitHeldella sp. 



Bellerophon sp. 



cf. Cyclora alia. 



Conularia sp. 



Platyostoma sp. 



Pleurotomaria sp. 



Loxonema sp. 



Modiolopsis sp. 



Mytilarca mytiliformis (Hall). 



Pterinea sp. 



