PART III 

 THE CROP REGIONS OF OHIO AND THEIR SIGNIFICANCE 



A. Topography and Drainage 



Ohio lies at the western edge of the Allegheny plateau. This 

 extends partly within the state, and constitutes the eastern and 

 southern three-fourths of it. The northwestern one-fourth is in 

 the Erie Plain. Southwest, the Allegheny plateau merges without 

 a definite line of separation into the Lexington Plain extending 

 northwest from Kentucky (see Fig. 7). In the extreme north- 

 west corner of Ohio is a low escarpment, separating the Erie Plain 

 from the Thumb Upland of Michigan. Thus the Erie Plain forms 

 a trough tilted toward Lake Erie. In Ohio the Erie Plain ranges 

 in altitude from 575 to nearly 1000 feet above sea level. (Geologic 

 Atlas, Columbus Folio pp. 1 to 4). The relief is, however, slight, 

 and it is on the whole a gentle rolling plain interrupted only by 

 low swells and morainic ridges. The Allegheny Plateau in Ohio 

 stands between 1000 and 1500 feet above sea level. It is tilted 

 southwestward and westward. The highest point in Ohio is at the 

 western edge of the plateau, near Bellefontaine in Logan County, 

 and is 1550 feet above sea level. In the eastern and southeastern 

 parts of the state, the plateau is so much dissected by valleys from 

 200 to 800 feet deep that but little of the plateau nature is discern- 

 able. The escarpment separating the plateau from the Erie Plain 

 is well marked in the northeastern and central part of the state. 

 The western ends of the escarpment are, however, obscure and 

 broken in two places by gaps which extend southward in the broad 

 valleys of the Scioto and Miami Rivers. 



The drainage of the Erie Plain and its immediate boundary in 

 Ohio, about 12,000 square miles, is into Lake Erie and so on into 

 the Gulf of St. Lawrence. The rest of the state, about 30,000 square 

 miles, is drained into the Ohio River and through the Mississippi to 

 the Gulf of Mexico. Ohio thus lies on the divide of the two great 

 continental drainage systems of Eastern America. The divide be- 

 tween these systems is on the whole rather level and inconspicuous, 

 resembling a rib of an enormous umbrella rather than the ridge 

 of a roof. Lake Erie is about 140 feet higher above sea level 



48 



