616 GEOLOGY OF OHIO. 



fuel can be obtained. The limestone lies in ledges fifteen or twenty feet 

 in thickness, whole acres of which are almost bare of soil. When trans- 

 portation shall be furnished by an east and west line of railroad along 

 the Sunfish valley, it is certain that a large business must grow up in 

 this manufacture. 



The limestone in these valleys is traversed by well-marked joints, 

 which are occasionally enlarged into deep fissures, as can be seen in the 

 bed of Sunfish Creek, in the neighborhood of Byington. 



The line of junction between the limestone and the overlying slates 

 can be distinctly followed through almost its whole extent in the county, 

 being unobstructed by Drift beds, and, to a great degree, by the products 

 of disintegration from the adjacent rocks. There are numerous locali- 

 ties where unsurpassed opportunities are furnished for the study of this 

 line of demarkation between Silurian and Devonian time. 



The limestone finally disappears at the mill site opposite Latham, 

 dipping steeply beneath the slates. It is not to be seen again this side 

 of the folds of the Alleghanies, its nearest point of emergence being on 

 the Niagara River, a few miles below Buffalo, New York. 



2. The next formation in ascending order is the well-known member 

 of the Ohio series designated by the geologists of the former Survey as 

 the " Ohio Black Slate," and known in the present Survey as the Huron 

 Shale. In the central portions of the State, and thence to the northward, 

 it is underlain by the Cormiferous limestone, but in the area now under 

 consideration it always covers, as has been already stated, the Greenfield 

 stone. Its place in the geological scale is made out with a little diffi- 

 culty on account of its paucity in fossils, but it seems to belong, on 

 stratigraphical grounds, to the Middle Devonian. 



The Huron shales make a very important element in the western half 

 of Pike county. Its whole thickness is shown in the hills of the west- 

 ern border. Its uppermost courses make the bed of the Scioto River, and 

 are nowhere seen to the eastward of the margin of the valley. 



In an excellent section just west of the county line, furnished by Slate 

 Knob, a thickness of two hundred and forty-eight feet was found by the 

 level; while in Fort Hill, two or three miles to the eastward, they were 

 found to be two hundred and fifty-six feet thick. The greatest measured 

 section gave three hundred and thirty-two feet. There is no doubt that 

 the formation increases in thickness to the eastward, and it is probable 

 that the average is not less than three hundred feet. 



All of the peculiarities of the formation are shown with great distinct- 

 ness in the western regions of the county. Its lower portions are quite 

 heavily charged with sulphuret of iron, and, indeed, a notable quantity 



