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



165 



The more western series of outcrops of the Belfast bed horizon, has 

 not furnished fossils, but in the intermediate region at High Banks, 

 south of Troy, annelid teeth were found in the upper courses of the 

 shales below the Belfast bed. 



The question arises, what do the annelid teeth indicate concern- 

 ing the age of the Belfast bed? The same species of annelid teeth as 

 those found in the Belfast bed occur also in the undoubted Lower 

 Silurian limestones, at the railroad bridge three miles west of Peebles, 

 where the Belfast bed is entirely absent. They occur also near the 

 top of the underlying shales at the High Banks, which twelve feet 

 farther down, and again three feet lower, include limestone courses 

 of undoubted Lower Silurian age. These occurrences suggest the 

 Lower Silurian age of the annelid teeth, and hence of the Belfast 

 bed. 



The presence of Halysites catenulatus therefore suggests an 

 Upper Silurian horizon, and the presence of the annelid teeth, a 

 Lower Silurian horizon. 



The next question which suggests itself is, what evidence of 

 Upper or Lower Silurian origin can be secured by closer observation 

 of the lithological features of the Belfast bed. The exposures of the 

 rocks below the Clinton, along the western exposures in Ohio are 

 quite instructive in this direction. At Ludlow Falls, under the 

 Clinton are found two and a third feet of blue, argillaceous, but quite 

 firm stone, in layers usually two to three inches thick. This is the 

 Belfast bed. Below it are five feet of a softer, more clayey blue 

 shale. At West Milton the material immediately beneath the 

 Clinton is a blue clay with shaly partings, 58 inches thick; then 8 

 inches of a hardened blue clay comparable to the Belfast bed in the 

 intermediate series of exposures, west of the more eastern line of out- 

 crops; beneath are 62 inches of blue shaley clay in the lower two feet of 

 which occur Lower Silurian forms of Of this (Platystrophia) biforata, 

 with fairly broad plications. At Lewisburg, along the creek about 

 half a mile south of town the Clinton is underlaid immediately by a 

 three inch course of hard blue limestone with Orthis occidentalis 

 and many branching Lower Silurian bryozoans; next come about 

 three feet of blue clayey shale beneath which are 4 inches of lime- 

 stone. Near Enterprise the Clinton is underlaid by 12 inches of 

 greenish clay, below which occur limestone fragments with Orthis 

 biforata, Orthis occidentalis and Tetradiunt. About two miles south 



