220 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
general it is to be noted that the three geological provinces above 
referred to may be divided, according to the origin and evolution of 
their surface features, into five distinct physiographic provinces, (see 
fig. 3) as follows: (1) the coastal plain; (2) the Piedmont plateau; 
(3) the Appalachian mountains; (4) the Appalachian valley; (5) the 
Cumberland plateau. Since the two last provinces are not of special 
interest in connection with the present problem, only the first three 
will be here considered. 
The coastal plain.— Passing inland from the Atlantic coastline, 
one crosses first the gently sloping surface of the coastal plain, rising 
from sea level at the coast, to an altitude of 250 or 300 feet a hun¬ 
dred miles or more farther west. Near the ocean this plain is not so 
maturely dissected as farther west, and the monotonous stretch of 
nearly level country is very striking. As the traveler nears the inner 
border of the plain, however, he is impressed with the greater degree 
of stream dissection, which is due in part at least to the longer time 
the land has here been subjected to erosion, it having been the first 
portion of the plain to rise above the waters of the ocean. 
The Piedmont plateau .— Continuing westward, the same gentle 
slope is maintained by the surface of the Piedmont plateau, a pene¬ 
plain developed on folded crystallines. As noted for the inner border 
of the coastal plain, stream dissection has destroyed much of the 
original surface, but the gently rolling uplands between the main 
streams preserve the characteristic features of the peneplain, and 
give a remarkably even skyline. Near the junction of the Piedmont 
plateau with the Appalachian mountain belt is encountered a feature 
of special significance in the present discussion. The west-bound 
traveler notes in places an escarpment which seems to mark the 
western limit of the plateau,— an escarpment which rises abruptly 
from the peneplain level to an altitude of from a few hundred to two 
thousand feet. In places this feature may be destroyed by erosion, 
or so complicated with mountain masses as to be indistinguishable, 
but where well developed, it forms a striking element of the topog¬ 
raphy. Leaving the level of the Piedmont plateau and ascending 
to the top of this escarpment, the observer looks westward out over 
another peneplain surface similar to the one just traversed, except 
that it slopes to the west, away from the top of the escarpment. Stand¬ 
ing thus at the eastern edge of the upper level, he seems to be at the 
junction of two peneplains, which incline away from him in opposite 
