DESCRIPTION OF SECTIONS 307 



A short distance south of the above exposure the strata containing 

 Platymerella manniensis outcrop at a level only a few feet higher than 

 the top of number 3 of the above section. Exposures of limestone equiva- 

 lent to some horizon of the Sexton Creek formation are numerous over 

 an area several square miles in extent between Channahon and Wilming- 

 ton, where the covering of Pleistocene deposits is thin. 



About 22 miles north of Channahon limestones corresponding in age 

 to the Edgewood and Sexton Creek formations are exposed in the banks 

 of Waubansia Creek, in the vicinity of Oswego, where they have quite a 

 similar development and contain similar fossils to those along the 

 Desplaines River. 



North of Batavia limestone of Sexton Creek age outcrops in several 

 places along the Eox River in the vicinity of Geneva, Saint Charles, and 

 Elgin. A representative section of the strata exposed in the quarry 2 

 miles south of Elgin is as follows : 



Section of Strata exposed in the Quarry 2 Miles south of Elgin 



Sexton Creek limestone. Feet 



3. Limestone, yellow, dolomitic, weathering into layers 2 to 4 



inches thick 4y 2 



2. Limestone, gray, appearing massive in the ledge, but weathering 



into thin layers 17 



1. Limestone, gray, with a number of chert bands near the middle 



part 15 



Borings on the floor of the quarry reached the top of the Maquoketa 

 shale at a depth of about 6 feet. No Edgewood limestone is present at 

 this place, nor is it known in northeastern Illinois north of Oswego. 



A zone in the upper part of the quarry exposure at Elgin, number 3 of 

 the last section, contains numerous casts of shells of several species of 

 Stricklandinia, and corresponds to the horizon of Stricklandinia in the 

 upper part of the exposure along Kankakee Eiver, and to the Strick- 

 landinia zone exposed at Hamburg, in Calhoun County, Illinois. The 

 species include 8. cf. triplesiana and forms related to the Anticosti species 

 8. davidsoni, 8. brevis, 8. lirata, and 8. salteri, besides the fossils Rhi- 

 nopora near verrucosa, Dinobolus sp., Leptwna rhomb oidalis, Sclwcher- 

 tella hanoverensis, Plectambonites transversalis var., Dalmanella elegant- 

 ula, Orthis fldbellites, Platystrophia daytonensis, Pentamerus oblongus, 

 Cyclonema daytonensis, and Illamus daytonensis. 



North of Elgin to the Wisconsin State line the western border of the 

 area of Silurian limestone is covered so deeply with glacial drift that no 

 outcrops of Alexandrian strata are known. 



