Cincinnati Society of Natural History. 



B. A Study of a portion of the Upper Silurian Roeks of South-eastern 

 Indiana, and their correlation with equivalent strata in Ohio. 



The Upper Silurian strata of Ohio have been more or less definitely 

 identified with various New York horizons. Only two formations are 

 richly fossiliferous. The lower one of these has been identified with 

 the Clinton, and the upper one, with the Niagara of New York. The 

 upper fossiliferous formation is a dolomitic stone, and at many points 

 in Ohio is burnt into a fine quality of lime. It shows abundant fossils 

 at Cedarville and at many other localities in Ohio. The lower portion 

 of this dolomitic stone is often less fossiliferous than the upper portion, 

 has a bluer color, comes out in more even courses, and contains a 

 greater abundance of Pentamerus oblongus. Hence the lower, less 

 fossiliferous dolomitic stone is distinguished as the Springfield rock, 

 while the upper more fossiliferous portion is called the Cedarville rock. 

 Both the Springfield and the Cedarville rocks contains Niagara fossils 

 of the type described from Illinois, near Chicago, and from Wisconsin, 

 near Racine. They have also many species in common with forma- 

 tions in New York and adjacent Canada, which are associated with 

 the Niagara. 



In Adams county and in portions of Highland county the 

 dolomitic Niagara rock is underlaid by a more argillaceous fissile 

 shale. This was identified with the Niagara shale of New York. 

 Even in the more northern counties of Ohio, where this horizon is not 

 occupied by a shale, but by an argillaceous stone forming courses of 

 moderate firmness often 4 to 8 inches thick, the rock is still called the 

 Niagara shale. Although sometimes quite firm, this stone is usually 

 not suitable for building purposes since it deteriorates under the influ- 

 ences of weathering. Since this formation is practically non-fossilifer- 

 ous, the chief reason for calling it the Niagara shale is its position 

 below the dolomitic rock which is undoubtedly Niagara, although 

 more of the type of the upper Niagara of New York. The fact that 

 this lower horizon is shaly in the south-eastern counties nearer the 

 Ohio river assisted in this determination. 



Beneath the " Niagara shale," of Ohio, whether shaly or not, 

 occurs a hard white limestone 3 to 5 feet thick, and then, lower down, 

 a very pure limestone, becoming more siliceous eastward, locally, in 

 the region of the Clinton conglomerates. This lower formation varies 

 from 10 feet m the west to 24 feet near Dayton, and 35 feet and more 

 in its most eastern exposures. It is the lower one of the formations 



