Geographie Character: Central Division. 103 
Floridan peninsula which on its west coast is lined with extensive mangrove 
swamps. The Gulf of Mexico is of large dimensions and its coasts are 
usually low. The region of the Mississippi delta is flat and consists of the 
material brought down by that stream. 
The Piedmont plateaus are west and northwest of the central portion 
of the Atlantic plain. The rocks which enter into the formation of them are 
mainly Archaean and are all more or less of metamorphic character. During 
Cretaceous time, these plateaus which extend southwest from New York Bay 
stood at sea-level and formed a peneplain. When the land was upheaved 
finally, the upheaval included the Piedmont region and this kind of disturbance 
has continued with intermission until the present time. A fall line separated 
the Piedmont plateaus from the coastal plain. The Susquehanna River, which 
enters Chesapeake Bay, is well marked by rapids at the fall line near its 
mouth and swift waters cross the Piedmont area and continue up into the 
mountain region. The Delaware, James, Roanoke, Yadkin, Savannah and Santee 
rivers, the latter formed by the junction of the Catawba, Broad and Saluda 
rivers, drain the Piedmont region and are characterized by rapids, or by more 
or less swift water, when they cross the fall line. The region is characterized, 
then, as a rolling country, with the plateau surface crowned by the ancient 
hills of granite, quarzite, slates and schists and cut into gorges and valleys 
with meandering channels and flood plains. 
The most important fact in the topography of the central portion of North 
America is the existence of a central comparatively low plain sloping 
towards the Gulf of Mexico from a watershed in close proximity 
to the Great Lakes. Eastward of the Mississippi valley is the Appalachian 
range of mountains and along the ocean the Atlantic coast plain. Westward 
of this central plain is the Cordilleran mountain system comprising three par- 
allel ranges, named respectively the Rocky Mountains, Sierra Nevada Mountains 
and Coast range. 
The Appalachian ranges belong to an ancient system of uplift. Volcanic 
materials have not since Mesozoic times invaded this region, which is in sharp 
contrast to the mountainous Cordilleran region where eruptive dikes and over-. 
flows of Tertiary and post-Tertiary age are found. The Appalachian system 
comprises the entire complex of mountains, valleys and tablelands which extends 
from northern New England generally southwest to the Gulf of Mexico. One 
very important break in the system occurs, occupied by the Hudson and 
Mohawk rivers. A depression of 152 feet (46 m) would be sufficient to permit 
the ocean to connect with the St. Lawrence valley via Lake Champlain. No 
other break in the Appalachian system is as complete as this and by this 
fact we are compelled to recognize that there are essential points of difference 
between the mountain complex to the northeast in New England and that 
lying to the south and southwest of the Hudson River valley. 
The New England mountain system is most irregular in its topography. 
Two great elevations are distinguishable, the Green and the White Mountains, 
