DELAWARE COUNTY. 287 



of the Olentangy, in the banks of a ravine the distance of a mile from 

 the river. For a considerable distance from this point, in descending 

 the Olentangy, the banks show frequent exposures of the limestone. 

 Near Mr. Wm. Case's quarry, five and a half miles below Stratford, the 

 black slate may be seen by ascending a little ravine that comes in from 

 the east. The section here is given in describing the Upper Corniferous. 

 Just at the county line the slate appears in full force again in the left 

 bank of the river, little streams bringing fragments from the west side 

 as well as from the east. A perpendicular exposure on land owned by 

 Granby Buell of about forty feet consists of about five feet of shale at the 

 bottom. It is also seen on the west of the Olentangy, by ascending a 

 ravine near the county line, on Archibald Wood's land, and again, by 

 ascending another ravine about three-quarters of a mile north of the 

 county line, on the land of F. Bartholomew, and it seems to extend about 

 two miles west of the Olentangy at its point of exit from Delaware 

 county. 



Olentangy Shale. — This name is given to that bluish and sometimes 

 greenish shale which is so extensively exposed in the banks of the 

 Olentangy River, in Delaware county, and which underlies the black, 

 tough, but thin beds of the Huron shale. It has a thickness of about 

 thirty feet. No fossils have been found in it. It is interstratified with 

 a little black slate, and in some of its exposures it bears a striking 

 resemblance, at least in its bedding, to the Huron shale. The section 

 which has already been given of its exposure at Delaware is the most 

 complete that has been taken, and very accurately represents its bedding 

 and characters wherever seen in the county. It lies immediately upon 

 a hard, blackish, sometimes bluish, crystalline, pyritiferous limestone, 

 or on the beds that have been denominated Upper Corniferous in reports 

 on the counties of Sandusky, Seneca, and Marion. In the county of 

 Franklin, and further south, it is said to be wanting, and the black slate 

 lies immediately upon the same limestone beds. It is also wanting in 

 Defiance county, the black slate there also lying immediately on the 

 beds that contain the only Hamilton fossils there yet discovered. This 

 shale embraces occasionally a course of impure limestone that has a blue 

 color and a rude concretionary appearance. On account of easy quarry- 

 ing, it is a constant temptation to the people to employ it in foundations. 

 It is found, however, to crumble with exposure after a few months or 

 years, and change into a soft shale or clay. Large blocks of it are washed 

 out from this shale just below Waldo, in Marion county, by the force of 

 the water coming over the dam at the mill, and have been somewhat 

 used by Mr. John Brundage, near Norton, in Marlborough township. 



