514 



Bulletin 316 



peach region about the town of Koshkonong, in Oregon county. George 

 Reeder, of the United States Weather Bureau, after a careful study of the 

 topography and cHmatic conditions, reaches the conclusion that the 

 immunity of the orchards in that vicinity from frost results from drainage 

 of the cold air away from the orchards, and, although the slope of the 

 land is slight, it is sufficient to ward off frost. 



The famous regions known variously as " thermal belts," " frostless 

 zones," or " verdant zones," found in certain mountainous districts of 

 North Carolina and elsewhere, result from air drainage. The verdant 



M/^r / 



Fig. 139. — Average date of last killing frost in spring 



zone in Macon county. North Carolina, in the valley of the Little Tennes- 

 see River, was described by Silas McDowell in 186 1. It lies between 

 300 and 700 feet above the valley floor, and the valley floor is about 

 2,000 feet above sea level. The breadth of this zone is about 400 feet. It 

 follows up the smaller tributaries of the river, and in the higher valleys, 

 where the valley floor is 3,900 feet above sea level, the verdant zone lies 

 between 4,000 and 4,100 feet. It is said that within this zone frost never 

 injures vegetation and the tendcrest grapes never fail to produce abundant 

 crops. A similiar zone is found in Polk county. North Carolina, on the 

 flank of the mountain spur adjacent to the valleys of the Blue Ridge. 



