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



A. The Belfast bed of Ohio, formerly called the Medina, with frequent 

 observations on the Clinton of Ohio. 

 The Clinton formation of Ohio is the lowest formation in that 

 state, belonging without question to the Upper Silurian. Between 

 the Clinton of Ohio and the upper fossiliferous beds of the Cincinnati 

 formation occur in many parts of the state a series of unfossiliferous 

 beds which it is difficult to assign definitely either to the Upper or to 

 the Lower Silurian. Quite frequently the upper part of these unfos- 

 siliferous beds consist of a firm rock breaking up and becoming shaly 

 parted after being exposed for a time to the influences of weathering. 

 Where fresh it has a bluish color, but where long exposed it is yellowish 

 or brownish. It has a massive structure in places, being made up of 

 layers 4 to 12 inches thick, with thin partings. Containing in addition 

 to lime a considerable amount of argillaceous material, it is in strong 

 contrast with the very pure Clinton limestones, which overlie it. It is 

 usually underlaid by blue clay or clay with shaly partings. It is 

 therefore, where typically developed, a horizon easily recognized. Its 

 typical development is beneath the eastern line of outcrops of the 

 Clinton in Ohio. It occurs for instance two miles south of Win- 

 chester, at Kelly's Mill on Branch creek, about three and one-half 

 miles southeast of Belfast, at numerous points near Belfast, at Sharps- 

 ville, at Todd's Fork north of Wilmington, at Spring Hill, dy 2 miles 

 west of the Todd's Fork locality, at Betty Heidy's quarry, 5^ miles 

 west of the Spring Hill locality and east of Oregonia, at Caesar's 

 creek, 4^ miles south of Xenia, at Goe's Station, 3^ miles southeast 

 of Cedarville, and at Donnelsville, 9 miles west of Springfield. Along 

 this eastern line of typical exposures few fossils have been found. Anne- 

 lid teeth have been noted at the various exposures near Belfast, at 

 Sharpsville and along Todd's Fork. At Sharpsville was found a species 

 of 0?this allied to the form which I have described under the name O. 

 calligramma in my papers on Clinton Group fossils. The valves show 

 however a greater number of plications and other variations, which 

 for the present make the fossil useless for purposes of correlation. At 

 the bridge exposure southeast of Belfast there was found an undoubted 

 specimen of Halysites catetiulatus. This species has never been re- 

 corded from the undoubted Cincinnati group in this state, Indiana or 

 Kentucky. It is on the contrary a fairly common fossil in the so-called 

 Clinton, immediately above. The occurrence of Halysites is there- 

 for strongly suggestive of the Upper Silurian age of this rock, and it is 



