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 Cormferous 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 
