484 GEOLOGY OF OHIO. 



the hills are clothed with the verdure oi June, and the dividing lines 

 will be as sharp and well-defined as if the woods had been laid out and 

 planted by the art of the landscape gardener. 



GEOLOGICAL STEUCTUEE. 



Although the entire surface of the county is covered deep in drift, or 

 its derivatives, yet the upheaval of the center exposes three formations- 

 of rock, and there is good reason to suppose that a fourth would be visible 

 but for the immense deposits of gravel in the Miami Valley. These for- 

 mations are Huron shale or black slate, shown in the hills aboHt the- 

 heads of Mad River, the Corniferous limestone, best seen in the Belle- 

 fontaine, Macachack and Middleburg quarries, and the water-lime rock, 

 esposed in one place on the Machachack, and in numerous ones in the- 

 neighborhood of Belle Centre and Northwood, while it is the Niagara, 

 that is supposed to lie under the drift in Miami Valley. 



The Huron Shale, lying highest, and being from its soft, laminated 

 structure most subject to the wear of the elements, has been cat dowrt 

 by frost and water until only two irregular islands are left, where out- 

 lines are shown, approximately, on the ntap. 



The smaller of these islands, lying directly east of Bellefontaine, in 

 Rush Creek, Lake, and Jefferson t&wnships, is the last outlier of its for- 

 m.ation east of the anticlinal axis of the State, or rather, it is directly 

 on, the crown of the arch. Its northern end is hidden under the D-rift, 

 bu>t must lie some where near Harper, and the southern is found about 

 three miles south-west of Zanesfield, where a deep cut was begun through 

 it some years since on the line of the Delaware Railroad, giving a length 

 of about nine miles, with an average width of some two and one-half or 

 three miles. 



The second and larger island lies east of Zanesfield and West Liberty^ 

 and underlies Pickreltown and Wickersham's Corners, in Rush Creek^ 

 Jefferson, Perry, Monroe, and Zane townships, with a spur extending 

 into the northern edge of Champaign county. It is about twelve miles 

 iong by three wide,, and within its limits are to be found the finest and 

 most characteristic exposures. 



The thickness of the slate on the line of section A B is 110 feet under 

 the western or Hogue's summit, by actual measurement with the level, 

 and 136 fee-t, by careful barometrical estimate, under Wickersham's- 

 Corners. 



Immediately below these Huron Shale islands lies one large island of 

 Corniferous limestone, which can be traced through Rush Creek, Jeffer- 

 son, Perry, Zane, Mony;oe, Liberty, Lake, Harrison, and McArthux town- 



