GEOLOGICAL PAPERS. 103 



The presence of such remnants of pre-CHnton Silurian forma- 

 tions as the Channahon and Essex limestones furnish abundant 

 evidence that, even where apparently conformable, the Niagara 

 limestone in northern Illinois is separated from the underlying 

 Maquoketa (Richmond) beds by an important stratigraphic break 

 of very considerable length. 



1. Note : In a private letter in which the statement credited to Dr. 

 Foerste was made, he says that this suggested differentiation of the faunas 

 in the strata at Clifton, Teimessee, was from memor>" only, this subdivision 

 of horizon not being suspected at the time the fossil collection was made. 



THE EASTWARD EXTEXSIOX OF THE SWEETLAXD 

 CREEK SHALE IX ILLIXOIS. 



By J. A. Uddex, 



Universit)' of Texas, Petrolia, Tex. 



In 1S98 I had occasion to examine and describe a deposit of 

 shale which occurs under the Pennsylvanian. in Muscatine Coun- 

 ty in Iowa. It overlies unconformably the Cedar Valley limestone 

 in this locahty and its entire thickness is only about forty feet. 

 It is a shale that is quite distinct from any shale in the coal meas- 

 ures. It is more evenly developed than the latter, and single layers 

 in it, only a few inches thick, may be traced for several miles. 

 The upper part of the shale has a grayish green color. The lower 

 part is dark, and it contains some strata of dolomitic limestones 

 at the base. These basal layers contain teeth of Ptyctodus eal- 

 ceolus, often in abundance. The lower half of the formation as 

 here developed also contains other fossils, such as : 



Lingiila, sp. undet. 



L. cf. melie Hall. 



Linguia, cf. nuda Hall. 



Lingiila subspatulata M. and W. (?) 



Spathiccaris emersoni Clarke. 



Solenocaris strigaia Meek. 



Ptyctodus calccolus M. and \V. 



Rhynchodus, cf. excaz-atus Xewb. 



Synthetodus. 



Gastcropods. 



There is also present in considerable abundance the fossil known 



as Sporangitcs huroncnsc. This fossil is supposed to be a spore 



of some paleozoic tree, and consists of brown circular discs 



nearly too small to be seen by the unaided eye. In some layers this 



is present in such abundance as to give the shale a brownish color. 



The spores consist of a bituminous substance, and when submitted 



to a distilling heat the shale gives out a considerable percentage of 



