150-350 



234 INDEX TO THE STRATIGEAPHY OF NORTH AMERICA. 



Northern Ohio. Southern Ohio. Feet. 



[Hillsboro sandstone . . . 



Cedarville limestone... 



, . „ Springfield limestone.. 



"Niagara group L^^^^ jj^^^^ limestone. 



Osgood beds 



Dayton limestone 



Clinton limestone v 10-50 



Northern Ohio. Southern Ohio. 

 Medina shale (?) Belfast bed (5 feet) 50-150 



Detailed descriptions of the formations are given by Prosser^" in another 

 article. 



The Silurian and Devonian limestones of Tennessee and Kentucky are dis- 

 cussed by Foerste ^^^^ in some detail. He locates the Cincinnati anticline in these 

 States and says: 



This fold was in existence in early Devonian, if not in Silurian times. No Silurian forma- 

 tions occur along the crest of the fold in central and southern Kentucky, or in northern and 

 central Tennessee. * * * Surrounding this area and overlapping the Ordovician on the 

 flanks and ends of the anticHne are Silurian strata, the total thickness of which diminishes on 

 approaching the crest of the fold. 



The result is that Devonian strata rest on Silurian formations along the flanks and ends 

 of the anticline, but along the crest, from north of central Kentucky to southern Tennessee, 

 they rest directly on the Ordovician. * * * 



There is * * * a remarkable similarity in the characteristics shown by the most 

 southern Silurian exposures in Kentucky and the most northern outcrops in Tennessee. This 

 similarity extends even to the minor subdivisions of the group. * * * 



The most accessible of the Silurian sections in northern Tennessee is that along the Louis- 

 ville & Nashville Railroad, near South Tunnel, about 10 miles south of the Kentucky border. 



In several railroad cuts Foerste found the Chattanooga shale (Devonian) 

 resting upon the Waldron shale (Silurian), and that in turn upon the Laurel lime- 

 stone, 28 feet thick. 



Both in Kentucky and Tennessee the top of the hmestone [Laurel], especially the oohtic 

 layer, contains fossils which also occur but in greater abundance in the Waldron shale. At 

 South Tunnel WhitjieldeUa nitida occurs in the oolitic layer. Orthoceras amycus is found near 

 the middle of the Laurel limestone. Pisocrinus gemmiformis is common near the base. This 

 fossil is especially abundant at a fourth railroad cut. * * * 'pjjg base of the formation 

 is here a crinoidal limestone. In Indiana and northern Kentucky Pisocrinus gemmiformis 

 occurs abundantly, both in the base of the Laurel limestone and in the limestone layers placed 

 at the top of the Osgood beds. Farther south it becomes difficult to determine where to draw 

 the Une between the limestone layers belonging to the Laurel and those referred to the top 

 of the Osgood beds. In Tennessee it is impossible to make such a separation, and here all of 

 the limestone section is referred to the Laurel. 



Foerste mentions localities where the Laurel limestone rests on clayey material 

 which stratigraphically undoubtedly represents the Osgood shale of Kentucky 

 though lithologically it is much less shaly. 



At South Tunnel the Clinton is first seen in the form of fragments of fossiliferous chert. 

 * * * The lower part of the Clinton is a bluish limestone, containing much less chert and 

 only a few fossils. It resembles so much the top of the immediately underlying Ordovician 

 rock, in which fossils are also scarce, that it requires patience to determine where to draw the 

 'line between the Silurian and the Ordovician rocks. 



