ALTITUDE AND TOPOGRAPHY. 67 



greater part of Indiana and large areas in Ohio fall between 500 and 1,000 

 feet. The only portions of the region falling below 500 feet are a narrow 

 strip in New York, on the south border of Lake Ontario, and a jDortion of 

 the valley of Ohio River and the lower courses of its tributaries in southern 

 Ohio and Indiana. Near New Albany, Ind, the 500-foot contour recedes 

 a few miles from the Ohio River into the lowland formed in the Devonian 

 shale, but returns to the river just below that city. 



TOPOGRAPHY. 



In the description of the rock formations it was shown that all the 

 earlier formations from the Trenton group up to the Hamilton contain a 

 large -amount of limestone and easily disintegrated shale, while the later 

 formations contain very little limestone, and often are made up largely of 

 resistant sandstone. This difference in constitution and texture has resulted 

 in a marked difference in topography: The formations which contain a large 

 amount of limestone or soft shale have become broken down to a markedly 

 lower elevation and a more even surface than the resistant sandstone. 



The sandstone or hilly country, being mainly on the borders of the 

 Appalachian Mountain system, occupies the southeastern part of the region 

 under discussion The border between it and the lower plain underlain by 

 shale and limestone may be roughly indicated as follows: From the Genesee 

 Valley at Mount Morris it takes a westward course, passing a few miles 

 south of Batavia and Buffalo, N, Y., to Lake Erie It follows the lake 

 border southwestward to the vicinity of Cleveland, Ohio, lying usually 

 but 5 to 10 miles south of the lake, though at the Grrand River Basin in 

 northwestern Ohio it extends southward about 40 miles. A short distance 

 west from Cleveland the hills bear away from Lake Erie to the vicinity of 

 the continental divide in Medina, Ashland, and Richland counties. From 

 near Mansfield in Richland County the border turns southward and main- 

 tains this course for nearly 100 miles, constituting the eastern rim of the 

 Scioto Basin. It then swings westward across northern Ross County, 

 passing a short distance north of the city of Chillicothe, and enters the 

 northern part of Highland County. Here it again turns southward and 

 passes through Highland and Adams counties into Kentucky, crossing the 

 Ohio River near the mouth of Brush Creek, a few miles above Manchester, 

 Ohio. 



On the borders of the Ohio the plain is so dissected as to appear less 



