342 A NATIONAL PLAN FOR AMERICAN FORESTRY 



States. Midsummer precipitation, although high on the average, is 

 irregular. At several places as much as 9 inches is recorded as having 

 fallen in 24 hours, and at one point there is a record of 22 inches 

 within 2 days. 



Snowfall is generally unimportant, running from a yearly average 

 of less than 5 inches along the seacoast of South Carolina to 30 or 40 

 inches on the upper Potomac watershed. 



The region is divided into three distinct physiographic provinces: 

 The coastal plain, the piedmont, and the Appalachian Mountains. 

 The coastal plain rises from sea level to between 200 and 400 feet at 

 the Fall Line, where it adjoins the piedmont. Considerably more 

 than half of the coastal plain is flat, and below 100 feet in elevation, 

 but with the rise in elevation westward the land becomes gently 

 rolling, and breaks into rather sharp differences in elevation between 

 the ridges and the stream bottoms. The piedmont plateau rises from 

 the Fall Line to elevations of 600 to 1,500 feet; the general topography 

 varies from gently rolling to somewhat broken. 



From the western boundary of the piedmont plateau the mountain 

 province rises, sometimes by as much as 2,000 feet in the space of 3 

 miles, to the summit of the Blue Ridge, which in the Carolinas is from 

 3,000 to over 4,000 feet above sea level. In the Virginias and Mary- 

 land the eastward flowing streams originate against ridges farther to 

 the west, and flow in narrow gorges through the Blue Ridge which is 

 here much lower in elevation than farther south. 



The soils of the coastal plain are predominantly sandy, but there is 

 considerable diversity as between the nearly pure sands of the Sand 

 Hills, and the loams and even silt loams of other localities. The 

 piedmont soils are predominantly deep clays, with some sandy 

 loams, clay loams, and silts, which are particularly subject to erosion. 

 The mountain soil types merge with those of the piedmont on the 

 slopes of the Blue Ridge. Although on the whole remarkably deep 

 for mountain soils, they are shallower, of lighter texture, and more 

 stony than the piedmont soils. West of the Blue Ridge in Virginia 

 many soils are derived from limestone and calcareous shales. 



EROSION 



Erosion, involving both deterioration of soil and the silting of 

 reservoirs and navigable channels, is the overwhelmingly important 

 watershed problem of the South Atlantic drainages, and one which 

 has reached very serious proportions on the piedmont plateau and in 

 adjacent portions of the other physiographic provinces. 



The clays, clay loams, and silts which characterize the piedmont 

 are subject to erosion wherever exposed by clearing or by lumbering 

 and fire. They are particularly subject to erosion when loosened by 

 plowing, and, as has already been stated, when robbed of organic, 

 material by long-continued cultivation or repeated forest fires. Silt 

 lands erode even more readily than the compact clays. Surface run- 

 off in time cuts tremendous winding gullies through such soils. 



The piedmont soils probably erode more rapidly under even the 

 most skilful cultivation than if the native vegetation had remained 

 undisturbed. Unfortunately great areas of these soils have been 

 handled with little skill. Thousands of fields in the piedmont have 

 been plowed up and down hill instead of along the contours, or in 



