ranges. Within this belt is precipitated nearly all of the moisture
contained in the atmosphere. The warm, humid westerly winds, driven
against the lofty and cool mountain sides, have their moisture suddenly
and rapidly condensed, and the rain-fall on their western slope is found
by measurement to be prodigious, reaching as high as sixty-five cubic
inches for the year, being equal in quantity to that falling in many
tropical districts, and greatly exceeding that of any other portion of
the United States. These mountains have a determining influence on the
climate, both of the coast and of that in the interior. They act on the
clouds as they sweep against and over them, like a comb, extracting all
possible moisture, leaving a cool, elastic, and arid continental
atmosphere for this central area under present review. The effect is at
once pronounced and everywhere visible. Less than two degrees of
longitude _east_ of these mountain ranges there is but about (taking the
whole line from the thirty-fifth parallel to the northern boundary) an
average fall of seven and a half cubic inches of rain, a difference of
over fifty-five cubic inches within the year, in districts separated by
less than one hundred miles in a straight line from each other. The
consequence is, that, while in one there is a luxuriant growth in all
kinds of vegetation, in the other barren plains (destitute of all except
the lowest forms of vegetable life) exist, with a gradual but slow
return, as the eastern course of the winds are followed, to that normal
condition which prevails in districts where an abundant supply of
moisture is furnished. This is not fully found till the western limit of
the third climatic division is reached, where again we see on all hands
a general distribution of rivers and forests over the whole of this
area, with copious rains at all seasons, and humid and cool conditions
of the atmosphere, following each other in rapid alternations; producing
what we have seen fit to call the Variable climatic district, embracing
the whole eastern half of the continent.