Nature of the Deformation. 79 
of the present valley ridges, while the present wind-gaps repre- 
sent the former baseleveled intervals between the monadnocks. 
In the plateau rezion south of the Crab Orchard mountains no 
areas of sufficient extent to be represented on the map remained 
unreduced. The peneplain in this portion of the province was 
less perfect than in some others and occasional slight elevations 
remain clearly above its general level. These are sometimes 
due to the attitude of unusually resistant beds, but more often 
to the accidents of erosion acting on tolerably homogeneous 
material. 
DEFORMATION OF THE CRETACEOUS PENEPLAIN. 
One of the most important conclusions contained in the pres- 
ent paper, in its bearings upon geomorphology, is the recognition 
of the nature of the deformation found recorded in the present 
attitude of the baselevel peneplains. It is that these ‘deforma- 
tions have been mainly produced by true orogenic movements 
affecting comparatively narrow areas along certain well defined 
axes ; that they were not epcirogenic or continental uplifts such 
as would preserve a peneplain in approximately its original hori- 
zontal position ; nor even, as suggested by Willis,* uplifts which 
broadly arched the surface across the whole expanse of the pro- 
vince; also that orogenic activity has not been continuous along 
any one axis nor always in the same direction, though the total 
effect of the intermittent motion has been to elevate the whole 
province. 
Deformations of the baselevel peneplains have been recognized 
in this and adjacent regions by other writers, especially Davis 
and McGee. Thus Davis has shown that the Cretaceous pene- 
plain in Pennsylvania, New Jersey and portions of New England 
is tilted seaward, but he has not located its axis of elevation ; 
also McGee has shown that in the southern Appalachians every 
subsidence has been greatest at the sea margin and every eleva- 
tion greatest in the interior, which implies a cumulative seaward 
tilting. The class of facts from which he derived his evidence 
did not enable him to locate the main axes of uplift, though 
he clearly recognized the transverse Memphis-Charleston axis, 
which will be more fully described on a subsequent page. 
* Topography and Structure of the Bays Mountains, Tennessee, by 
Bailey Willis: School of Mines Quarterly, vol. viii, 1887, p. 252. 
12—Nar. Grog, Maa., von. VI, 184. 
