TOPOGRAPHY. 11 



DRAINAGE. 



"Two-thirds of the state may be considered as forming a 

 part of the great Mississippi Valley, while about the north- 

 ern third is in the basin of the great lakes. The water-shed 

 which divides the streams flowing into Lake Erie from 

 those tributary to the Ohio, traverses the state from near 

 the north-east corner in a south-westerly direction as a low 

 ridge the greatest elevation of which is nowhere more than 

 1400 feet above the sea. This water-shed is lower in Ohio 

 than in Pennsylvania and New York." (Wheaton.) 



ELEVATIONS. 



The surface of Lake Erie is 573 feet above the ocean. 

 During low water the Ohio river is about 426 feet above the 

 ocean at the extreme south-west corner of the state, near 

 Gravel Pit, rising to 687 feet at Wells ville in Columbiana 

 county. The Ohio river at its lowest point is thus 147 feet 

 below the surface of lake Erie. The variations in the general 

 surface of the state range from those given above to 1540 

 feet, which elevation is reached in Logan county a short dis- 

 tance east of Bellefontaine, where two hills rise, the one to 

 1500 the other to 1540 feet above tide. A hill in Richland 

 county reaches an elevation of 1475 feet. Nowhere else does 

 the state reach 1400 feet elevation. It will thus be clear that 

 nowhere does altitude play any important part in the distri- 

 bution of the birds. 



EROSION. 



The lake Erie drainage plain is generally a gradual slope 

 northward, with gorges cut into the underlying shale and 

 rock by the larger streams, but without hills of any conse- 

 quence. The northern and western parts of the Ohio river 

 drainage plain is also level, but growing rougher as the 

 streams descend and enlarge, reaching a maximum of rough- 

 ness in the south-eastern and southern parts of the state. 

 The unglaciated region presents the greatest erosion and 

 consequently the highest ridges and deepest valleys. Here 

 the streams have cut completely through the upper coal 

 strata. 



