62 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
by tlie Alabama and Tombigbee Elvers, and though partly kept up by 
the Chickasawhay and Pearl Eivers, bends then south nearly to Baton 
Eouge. Up the Mississippi Valley it is carried nearly to the 35th par 
allel, and after sinking below the 33d, is carried again by the lied 
Eiver Valley beyond the 35th parallel in the Indian Nation, whence it 
bends around southwest approximately parallel to the Texas coast, till 
carried far out to the west along the Pecos and Eio Grande. 
The rest of the cotton-producing territory of the United States is 
included between the summer lines of 7G° and 80°, excepting where the 
Blue Eidge in Western North Carolina and Northern Georgia and the 
Cumberland Mountains of Tennessee cause a great southward exten- 
sion of the summer mean of G8° to 72°, and where, along the eastern 
slope of the Blue Eidge in North Carolina and Georgia, around its end 
in Alabama, and between the Blue Eidge and the Cumberland ranges 
in the valley of East Tennessee, and on the western slope of the Cum- 
berland in Middle and Western Tennessee and Kentucky, and south- 
ward on the water-shed between the Tombigbee and Yazoo in Missis- 
sippi, the mean summer temperature is between 72° and 7G°. 
In view of the probable influence of the winter temperatures in de- 
termining the place of hibernation of the cotton moth, it has been 
thought best to transcribe upon one of the maps accompanying this 
article the lines of equal temperature, during the winter months, for 
every fourth degree, from 28° to 72° Fahr. These lines, as well as the 
data upon which the above account of the climate of this region has 
been compiled, have been taken from the Smithsonian Contributions, 
Vols. XVIII, XX, and XXI. 
It will be seen that these winter lines show the comparative regular- 
ity of those of the annual means ; they are carried northward by the 
influence of the Gulf Stream along the Atlantic coast, and by the vari- 
ous large rivers in the west, while they are carried southward by the 
mountains and high table lands. 
The chart, however, presents all these facts much more clearly than 
can be done by any verbal description. 
Geological Sketch. — Through North and South Carolina, Tennes- 
see, and Georgia passes the great mountain chain of the Appalachians, 
terminating in Central Alabama. The most elevated parts of this chain, 
and its southeastern or Atlantic slopes, are formed of the crystalline or 
metamorphic rocks, while the opposite or northwestern slope is made 
up of the strata of the Silurian and other Paleozoic formations. 
Westward of the Appalachian region of elevation these Paleozoic 
rocks underlie the country to the central part of Texas, not, however, 
continuously through the cotton-producing States, but interrupted by 
one great gap, which reaches up the axis of the Mississippi Eiver as 
far as the mouth of the Ohio. 
