An Account of the Middle Silurian Rocks of Ohio and Indiana. 



175 



this coral layer is but very poorly represented in Mason county, not 

 at all in Fleming, fairly well in Bath county, but seventy-five feet be- 

 low the top of the Lower Silurian ; it occurs in Madison, also in Gar- 

 rard, where in places the top of the Lower Silurian is marked by an 

 irregular mass of limestone filled with Columnaria and Tetradium as 

 usual; the layer is quite well developed in Lincoln, better in Marion 

 and Washington; also in Nelson and Spencer, and these corals also 

 occur in Shelby and Henry counties, and in Oldham. 



It will be noticed that this bed is not well represented in the 

 northeastern counties containing the Lower Silurian. It does not 

 seem to have been noticed north of the Ohio, in Adams, Highland and 

 Clinton counties. If it be considered desirable to bring the Morris 

 Hill locality into relation with the great coral reefs of Kentucky which 

 there mark the close of. the Lower Silurian, this can be affected more 

 readily by imagining the coral reef to have once extended across some 

 of the more central counties, now exposing only Lower Silurian beds 

 of a lower horizon. From these counties the coral reefs must then be 

 supposed to have been removed by erosion in later times. I 

 rather doubt, however, the former existence in Ohio of a continuous 

 layer containing an abundance of stromatoporoid fossils, Tetradium 

 and Columnaria. These fossils are probably distributed here chiefly in 

 patches at somewhat varying horizons. One or two specimens of 

 Tetradium were found just beneath the Clinton south of Eaton, Ohio. 

 A stromatoporoid growth was fairly frequent about 3^ feet beneath 

 the Clinton, at Fair Haven. About 40 inches beneath the Clinton, at 

 the Enterprise locality, very large growths of Tetradium, similar to 

 those at Morris Hill, were found. At John Kneisly's farm on the 

 Smithville road, 2 miles southeast of Dayton, Stromatopota and Tetra- 

 dium occur 6 feet below the base of the Clinton in a clay bed. 



14. Marian Clark Farm. Lytle. — Southwest of Lytle, perhaps 

 half a mile across the country, is the farm of Dr. William Stokes. At 

 the spring house behind his residence a rock crops out, which, accord- 

 ing to Dr. Stokes, was indentified by Prof. Orton as the Dayton lime- 

 stone. It is a rotten rock, of uncertain character and presents, for 

 Dayton limestone, the anomalous feature of rather frequent fossils 

 shown in the form of exterior casts, the shells themselves having 

 disappeared. Following the lane southwards about a quarter of 

 a mile, the farm house of Marian Clark is reached. Directly east 



