Variations of Types. 73 
sists of the even crested ridges similar to those of Pennsylvania 
which have been so well described by Dayis.* As a rule the 
ridges of the southern Appalachian valley are remarkably even 
crested and are unquestionably the remnants of a plain. In 
many cases, however, more or less wide variations from the type 
are found. In some instances a continuous but irregular ridge 
seems to rise quite above the peneplain, while in others the 
wind gaps have a constant altitude and probably represent the 
old baselevel, while the intervening portions of the ridge rising 100 
to 300 feet higher stand, now as then, as a series of knobs above 
the general level. On the other hand, some ridges composed of 
less resistant rocks or occupying more exposed positions have 
been so reduced by subsequent erosion that no points along 
their crests reach the altitude of the peneplain. In reconstruct- 
ing the peneplain from the valley ridges, careful study is required 
to determine its true position, and in some regions considerable 
uncertainty attaches to the determination. On the whole, how- 
ever, the results obtained from the ridges are surprisingly con- 
cordant with those obtained in adjacent regions where the plain 
is better preserved. 
Smoky Mountain Type.—This type differs altogether from those 
previously described and consists almost wholly of baseleveled 
valleys. They prevail from the vicinity of Roanoke, Virginia, 
to Cartersville, Georgia, giving rise to some prairie-like country 
in the heart of the Smoky mountains. It was in these valleys 
that this peneplain was first recognized. Ina paper read before 
this Society in 1889 Willis described the baseleveled valley of 
the French Broad river as follows : + 
A broad amphitheater lies in the heart of the North Carolina moun- 
tains which form its encircling walls; its length is forty miles from north 
to south and its width ten to twenty miles. At its southern gate the 
French Broad river enters; through the northern gate the same river 
flows out, augmented by the many streams of its extensive watershed. 
From these water-courses the even arena once arose with gentle slope 
to the surrounding heights. . . . But that level floor exists no longer. 
In it the rivers first sunk their channels, their tributaries followed, the 
gullies by which the waters gathered deepened, and the old plain was 
thus dissected. It is now only visible from those points of view from 
* The Rivers and Valleys of Pennsylvania, by W. M. Davis: Nat. Geog. 
Mag., vol. i, pp. 183-253. 
+ Round about Asheville, by Bailey Willis: Nat. Geog. Mag., vol. i, pp. 
291-300. 
