380 A KATIONAL PLAtf FOE AMERICAN FORESTRY 



Within the Cumberland Plateau, the Cumberland, Kentucky, Big 

 Sandy, and Tennessee Rivers have carved out topography of a highly 

 dissected and mountainous character. Slopes are steep, and ridge 

 tops reach elevations of 4,000 feet. To the northeast the Kanawha, 

 Monongahela, and Allegheny Rivers have dissected the Allegheny 

 Plateau in similar fashion, but the elevations reach only to about 

 3,200 feet in Pennsylvania. The Blue Ridge in eastern Tennessee 

 and North Carolina attains the highest elevations east of the Rocky 

 Mountains. From a base of about 1,600 feet in the Appalachian 

 Valley, the Ridge rises to high mountainous country containing some 

 40 peaks over 6,000 feet in elevation the highest of which, Mount 

 Mitchell, is 6,684 feet. Farther north in Virginia, the Blue Ridge 

 reaches an elevation of about 4,000 feet. 



SOILS 



In the more level northern and northwestern portions of the Ohio 

 River Basin, the soils are of glacial origin. They are derived from 

 glacial flour and drift resulting from the grinding of limestones, 

 shales, and sandstones. For the most part they include loams, silt 

 loams, and loamy clays, but in places rather light sandy soils are 

 found. They have not developed the porosity characteristic of much 

 older soils. 



Most of the rest of the basin contains residual soils formed in place 

 by the weathering of underlying rock formations. Exceptions are the 

 alluvial soils along stream bottoms and river benches, and certain 

 areas of loessial soil in western Kentucky, southern Illinois, and adja- 

 cent Indiana and Ohio, along the lower portions of the Wabash, Ohio, 

 and Tennessee Rivers. Large areas of weathered clays, loams, and 

 sandy loams in the hilly and Appalachian Plateau provinces have 

 been derived from shales, limestones, and sandstones. In the blue- 

 grass country of Kentucky and the central basin of Tennessee, the 

 soils are derived from limestone. In the Blue Ridge province the 

 soils are derived from granites, gneisses, schists, and other crystalline 

 rocks which upon disintegration yield light-textured soils. The 

 Appalachian Valley contains soils derived in large part from limestone. 



PRECIPITATION 37 



The average annual precipitation varies from 35-40 inches on the 

 minor drainages north of the Ohio River to 60-70 inches in the Blue 

 Ridge headwaters of the Tennessee River. Throughout most of the 

 lower hilly portion of the basin in Tennessee, Kentucky, and West 

 Virginia the annual rainfall frequently reaches 45-50 inches. Ex- 

 tremes of recorded precipitation range from 19 inches in Illinois to as 

 high as 120 inches in the Great Smoky Mountains of North Carolina. 



A relatively small part of the total precipitation comes as snow. 

 The heaviest average annual snowfall, approximately 80 inches, 

 occurs on the headwaters of the Monongahela and Kanawha Rivers. 

 The lowest snowfall is found in the Tennessee River Basin. The 

 average fall of snow north of the Ohio River is about 25 inches. 



As a rule, precipitation is well distributed throughout the year, 

 with heavier monthly averages from December to March or April, 



" Precipitation records cited are taken from Precipitation and Humidity, by J. B. Kincer, U.S. Dept. 

 Agr. Atlas of Amer. Agr. pt. II, A. 1922. 



