SNYDER CREEK SHALE. 37 



drab shale, with interbedded bands of shaly limestone, highly 

 f ossiferous; the middle member consisting of a light drab, 

 argillaceous limestone with few fossils, mostly remains of Cri- 

 noidea; the upper member consisting of a light gray, siliceous 

 shale, this like the lower member being highly fossiliferous." 

 South of Fulton about six miles the formation is about 25 feet 

 thick. He lists 34 species of fossils and indicates the species 

 that are common to the Craghead and the Lime Creek shale 

 and Cedar Valley limestone of Iowa. 



On account of the meagreness of Gallaher's description and 

 the lack of a Snyder Creek on maps of Callaway County, the 

 writer had used Craghead Creek in preference to Snyder Creek, 

 but a communication from Mr. David White gives the opinion 

 of the committee on nomenclature of the United States Geological 

 Survey that Snyder Creek has the better standing. In the 

 interest of harmony the writer is adopting the name Snyder 

 Creek. 



In 1860 Swallow 1 described several species of fossils from 

 the Snyder Creek shale of Callaway County, but called the 

 shales Hamilton. 



Relationships and Distribution. — The Snyder Creek seems to 

 be conformable on the Callaway and has not been found resting 

 on any other formation. It varies greatly in thickness and its 

 extent is decidedly patchy, the latter being due to erosion pre- 

 ceeding the advance of the Mississippian seas. Its entire extent 

 is in Callaway and Montgomery counties and it probably is not 

 greater than 200 square miles, while the area of outcrop probably 

 does not exceed 50 square miles. 



The Snyder Creek shale was deposited in a narrow bay 

 which extended southward from Iowa but did not reach much 

 south of the Missouri River and seems to have been less than 

 50 miles wide at the south end. Though the formation reaches 

 a thickness of 63 feet or more it rarely exceeds 25 feet and in 

 many places is less than 10 feet. The map of Callaway and 

 Montgomery counties shows its extent as accurately as our 

 methods of mapping allowed. 



Greger called attention to the close relationship of the Snyder 

 Creek fauna with those of the Lime Creek shale and Cedar 

 Valley limestones of Iowa and the fossils listed and figured in 

 this report emphasize the relationship with the Lime Creek 



'St. Louis Acad. Sci., vol. 1, pp. 635-660. 



