62 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 



by the Alabama and Tombigbee Elvers, and though partly kept up by 

 the Chickasawhay and Pearl Rivers, 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 Red 

 River 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 Rio Grande. 



The rest of the cotton-producing territory of the United States is 

 included between the summer lines of 70° and 80°, excepting where the 

 Blue Ridge in Western North Carolina and Northern Georgia and the 

 Cumberland Mountains of Tennessee cause a great southward exten- 

 sion of the summer mean of 68^ to 72°, and where, along the eastern 

 slope of the Blue Ridge in North Carolina and Georgia, around its end 

 in Alabama, and between the Blue Ridge 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 76°. 



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 Hues, 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 j 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 Carolioa, 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 crystalliue 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 River as 

 far as the mouth of the Ohio. 



