tawm.j OHIO KIVKR TO CHICAGO. 293 



clay manufacturing center in the State in the several lines above 

 noted. 



To the west of Zanesville and extending to the north and west as 

 far as Chicago Junction* 1 the Sub-Carboniferous series, consisting of 

 conglomerates, sandstones, and shales, and containing an abundant 

 fauna, admitting of several distinct subdivisions, occupy the country 

 traversed by the railroad. The conglomerate portion of the series has 

 been cut through by the Licking River between Zanesville and New- 

 ark and is well exposed in the picturesque gorge traversed by the rail- 

 road between these two points. 



Near Newark the great terminal moraine'" which marks the south- 

 ern extension of the Drift is crossed and the drift-covered area is 

 entered. 



The sections exposed between Newark and Chicago Junction agree 

 with those hist named, but the rocks appear at comparatively few 

 points. 



At Chicago Junction the basal rocks beneath the drift belong to the 

 black sliale division of the Devonian. The drift beds are here LOO or 



moie feet in thickness. 



Near Tiffin' 7 -' 1 the first exposures of underlying Devonian and Silu- 

 rian limestones are met with. They are found mainly in the valleys . 

 from which the mantle of the drift has been removed by erosion. 

 Bere begins the low anticlinal arch upon which the great accumula- 

 tion of gas and petroleum in northwestern Ohio has been proved to 

 depend. The central portion or summit of the arch is crossed between 

 Fostoria 21 and North Baltimore." Its structure is shown in the accom- 

 panying diagrammatic sections, (Figs. 8-10) the extremes of which are 

 about30 miles (48 km.) apart on the approximately north and south line 

 of the axis of the arch. 



The surface rock of the gas-producing portions of the arch is Niagara 

 (Wenlock) limestone; of the oil-producing portions, the surface rocks 

 are mainly Lower I leldeiberg (Ludlow) limestones. 



The oil and gas districts are flat lying regions, the extremes of the 

 surface elevations of several hundred square miles not exceeding 50 

 feet (16 in. i. The general level may betaken as 750 feet (225 m.) above 

 tide. The reservoir of gas and oil lies L,000to 1,300 feet (300 to 400 m.) 

 below the surface. At Fostoria and again at a point <> miles beyond 

 North Baltimore, the surface of the oil-bearing rock is nearly 500 feet 

 (150 in.) below tide level. At Bloomdale, on the axis of the arch, it is 

 300 feet (90 m.) below tide. The measurements afforded by the drill 

 indicate a gentle arch in the producing bed; when it is reached at .->()(> 

 feet <»r more below tide, it is found charged with salt water. From 400 to 

 450 feet below tide, it carries oil; at higher levels gas is found 



