THE CLIMATE. 27 



succeeding morning shows a heavy hoar frost; vegetation is utterly killed, including 

 all manner of fruit germs, and the landscape clothed in verdure the day before, now 

 looks dark and dreary. 



It is under precisely this condition of things that the beautiful phenomenon of the 

 "verdant zone," or " thermal belt," exhibits itself upon our mountain sides, com- 

 mencing at about 300 feet vertical height above the valleys, and traversing them in a 

 perfectly horizontal line throughout their entire length, like a vast green ribbon upon 

 a black background. 



Its breadth is 400 feet vertical height, and from that under, according to the degree 

 of the angle of the mountain with the plane of the horizon. Vegetation of all kinds 

 within the limits of this zone is untouched by frost; and such is its protective influence 

 that the Isabella, the most tender of all our native grapes, has not failed to produce 

 abundant crops in twenty-six consecutive years; nor has fruit of any kind ever been 

 known within these limits to be frost killed, though there have been instances where 

 it has been so from a severe freeze. The lines are sometimes so sharply drawn that 

 one-half of a shrub may be frost killed, while the other half is unaffected. 



The same writer states, further, that — 



The thermal belt must exist in all countries that are traversed by high mountains 

 and deep valleys, as the natural causes that produce it are as infallible as those which 

 produce the rainbow in the clouds, and the only reason why its visible manifestations 

 are peculiar to our southern Alleghenies is the fact that their precocious spring vegeta- 

 tion is sometimes killed by frost, while the same thing does not happen in the moun- 

 tains farther north. 



The above statement that "the thermal belt must exist in all 

 countries traversed by high mountains" may be too general, and the 

 ultimate causes which produce it may not be as simple as this writer 

 appears to think, though doubtless the explanation is contained in 

 the influences which produce a stratification of air at different tem- 

 peratures. However, the important fact to be noted is that in the 

 mountain regions under consideration this green belt does exist to a 

 greater or less extent and contributes its portion to the natural 

 advantages for fruit growing which the region possesses. 



Late spring and early fall frosts are other important factors to be 

 considered in studying the climatic conditions of a section with 

 regard to its suitability for fruit growing. Frequently it becomes a 

 matter of local consideration, as when there are "pockets" or valleys 

 into which cold air settles and from which it can not readily escape. 

 Such places are subject to unseasonable frosts. In the application 

 of this feature to the regions in question it is sufficient to say that as 

 a whole there is comparative freedom from such frosts. It some- 

 times happens that during the winter, mild weather which causes the 

 swelling of the buds is followed by disastrous freezes, but the more 

 favorably situated portions of these regions may be considered as 

 relatively free from such dangers and as little subject to extremes of 

 temperature as any of the more important fruit-growing sections east 

 of the Rocky Mountains. 



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