68 Hayes and Campbell— Appalachian Geomorpholog y. 
certainty the more prominent features over the greater portion 
of the province. In. some portions lack of data prevents the 
identification and correlation of these forms, but it is probable 
that further study will show the same features there as in the 
better known regions. The identity and practical continuity of 
certain topographic forms have been clearly proven through the 
major portion of the southern Appalachian province, and by 
other writers across Pennsylvania, New Jersey and the greater por- 
tion of New England, so that the conditions and agencies which 
produced them ane have prevailed uniformly over wide areas. 
In addition to these principal topographic forms, there are 
many minor features which doubtless record brief and local 
conditions, but in most cases the data at hand are not gnats 
for their de anmatacielem, 
Inferences from the observed topographic forms back to the 
conditions under which they were produced necessarily involve 
elements of uncertainty, and the writers are fully aware that 
some of their conclusions are open to question and may be mod- 
ified by further study. 
The classification of the main topographic features of the 
province is as follows: 
1. Elevations standing above the Cretaceous peneplain. 
2. Deformed Cretaceous peneplain. 
d. Intermediate erosion slopes. . 
4. Deformed Tertiary peneplain. 
5. Post-Tertiary erosion slopes. 
Of these five classes the two baselevel peneplains are most 
important to the student of geomorphology, for they render it 
possible to interpret the meaning of the other topographie fea- 
tures and to fix the dates of their origin in geologic time. 
™ 
ELEVATIONS STANDING AS8OVE THE CRETACEOUS PENEPLAIN. 
The oldest topographic forms found in the southern Appa- 
lachian province are those portions of the land which were not 
reduced to baselevel during the long period of Cretaceous ero- 
sion. These summits may possibly mark the position of a still. 
earlier baselevel peneplain; but if so, the remnants are so few 
that we are unable to reconstruct the ancient plain. Protected 
by a favorable location with reference to drainage lines or com- 
posed of exceptionally durable rocks, they stood during the 
formation of the Cretaceous peneplain in low relief above the 
