TEMPERATURE OF THE COTTON SEATES. 
61 
those parts where this percentage is 10 and above have a summer rain- 
fall below 14 inches, and a winter rainfall above 12 inches. 
Temperature. — The distribution of heat in the cotton States is 
nearly normal, as the isothermals follow approximately the parallels of 
latitude, the departures from this regularity being due (1) to the heat- 
ing effect of the Gulf Stream, by which the lines of equal temperature 
are elevated or deflected northward along the Atlantic coast; (2) to 
the cooling effect of the mountains, which causes a depression south- 
ward of these lines, as may be seen in the vicinity of the Appalachians; 
and (3) to the accumulation of heat in valleys, which carries the iso- 
thermaLa up these valleys, often to considerable distances beyond their 
normal position. With these general principles in view, it will be easy 
to understand the temperature distribution in the region of which we 
are writing. 
The mean annual temperature line of 68° Fahr. runs nearly parallel 
with the southern coasts of Alabama, Mississippi, Louisiana, and Texas, 
where these coasts have an east and west direction, and at no great dis- 
tance north of this shore line. In Texas it is carried up the Rio Grande 
Valley, beyond the 102d degree of west longitude. 
The line of 04° follows approximately the parallel of 33°, running 
north of it near the coast in North and South Carolina, because of the 
Atlantic Ocean; south of it in Georgia and Alabama, because of the 
influence of the Appalachian chain ; it is carried upward by the Missis- 
sippi and Bed River Valleys, bending downward on each side of them, 
being deflected far to the south beyond Red River, in Central Texas, 
by the influence of the western mountains. 
The line of G0°, starting from the coast of North Carolina a little 
north of the 30th parallel, crosses that State diagonally to the eastern 
foot of the Appalachian range, around the southern end of which it 
sweeps in a great curve which passes below Talladega in Alabama, and 
bends northwestward to New Madrid, Mo., whence it runs westward 
approximately along the 3Gth parallel through the Indian Territory 
into Texas, till turned southward like the preceding iu the western 
part of that State. 
The isothermals between 52° and 50° lie generally north of the cot- 
ton States, except in the Appalachian region of North Carolina, Ten- 
nessee, Georgia, and Alabama, and the central parts of Tennessee and 
Kentucky, but in none of these localities is the production of cotton 
on any large scale, except in Western North Carolina, the valley of the 
Chattahoochee in Georgia, that of the Tallapoosa, Coosa, and Tennes- 
see in Alabama, and a part of the central basin of Tennessee, where 
the mean annual temperature is between 5G° and G0°. 
The isothermals for the summer are far less regular than those of the 
year. Thus the summer line of 80°, starting at the coast near Charles- 
ton, runs westward to Macon, Ga. ; thence south to Tallahassee, Fla. ; 
thence diagonally across Alabama to Tuscaloosa, to which it is raised 
