20 APPALACHIAN AND WHITE MOUNTAIN WATERSHEDS. 



This kind of erosion occurs on close-grained, compact clay soils, the 

 particles of which chng together firmly and resist the do^vnward 

 cutting of small currents of water. 



Another type of erosion results in parallel gullies extending straight 

 up and down the slopes. As these gulKes grow deeper they ^\-iden, 

 the smaller ones are obliterated by the larger until they become of 

 huge size, their bottoms shaip, their sides steep, and their edges 

 irregular and jagged. Such erosion results from clay soils of homo- 

 geneous texture and somewhat softer and more loamy than the type 

 mentioned above. It is a very common type, and the process once 

 started can be stopped only with great difficulty. It nearly always 

 results in the early abandonment of the field on which it begins. 



Of all tj-pes of erosion, that of gullying, in which rapid down-cutting 

 is accompanied by undercuttiug and caving, is the most rapid ia its 

 progress and the most difiicult to check, as well as the most destructive 

 m its effects. This type occurs in soils of relatively soft micaceous 

 subsoil. The surface may be a fairly compact clay that offers mod- 

 erate resistance to water, but once broken a gully results in the soft 

 subsoil. It rapidly deepens, the micaceous material on the sides 

 is easily undermined and slips in, leaving vertical or overhanging 

 walls. Into such gullies many square yards of soU may cave during 

 a single heavy rain, and as the decomposed micaceous material is 

 usually scores of feet in thickness such gullies frequently become 

 chasms of great depth and width. This kind of erosion when started 

 on cleared land may advance into a forested area and undermine 

 even the largest trees. The rocks which produce soil subject to this 

 kind of erosion are found over a large part of the Southern Appa- 

 lachian region, and especially in the Blue Ridge Mountains. 



Still another type of erosion is that started by small landslides, 

 which occur on steep slopes when the soil is saturated during periods of 

 prolonged rainfall. Such landslides are often started by the tramp- 

 ling of cattle over the steep slopes during wet weather. One animal 

 in climbing up or down a slope may start a number of such slides, 

 each of wmch usually grows m width and length and soon makes a 

 great bare scar in the field. 



The soils subject to serious erosion are very extensive in the 

 Southern Appalachian region. Where on such soils nature has 

 placed a forest that brings about a balance between rainfall and 

 run-off, the danger in widespread clearing is obvious. The loss 

 resulting from erosion means not only the loss of the soil from the 

 fields; it means also the loss which has already been described in the 

 failure of v/ater power and navigation. 



MINING. 



While in the Blue Ridge and Great Smokies no valuable coal depos- 

 its are laiown to exist, these mountains have a great variety of min- 

 eral resources. Many of theni have never been developed, while 

 others have become the basis of important mining operations. Large 

 investments have been made in the mining of copper, marble, mica, 

 corundum, talc, asbestos, slate, kaolin, and other minerals, and the 

 mineral products are said to amount to several million dollars 

 annually. 



Such mining as is carried on does not require large quantities of 

 timber, since but a small part of it is underground mming, and some 



