200 DISCUSSION OF THE DESICCATION QUESTION. 



The effect of a mountain range in entirely cutting off the precipitation 

 from another one parallel with and adjacent to it, but on the leeward side, 

 as respects the prevailing wind, has already been alluded to, in the case of 

 the Sierra Nevada and the Inyo Mountains.* Where several ranges run 

 parallel with each other, each one farther to the leeward being somewhat 

 higher than the more windward ones, the result is that the precipitation 

 is distributed among them all, in the form of rain on the lower ranges, and 

 in that of snow on the higher, if these latter extend above the snow-line. 

 This is well exemplified in the case of the Noi'thwestern Himalaj-an Moun- 

 tains, whicli rise from an intensely hot and dry country at their base, in a 

 series of parallel chains, the whole breadth of which is not far from 300 

 miles. The Outer (or lower) Hills — the Sub-Himalayas, as they are also 

 called in the reports of the Government Geological Survey — receive their 

 precijiitation in the form of rain, and in larger quantity as the successive 

 chains rise higher and higher ; when we reach a sufficient elevation snow 

 takes the place of rain wholly or in part ; and, finally, the culminating range 

 is capped with glaciers surpassing even those of the Alps in magnitude. 



As has been seen above, shores — especially those rising in bold moun- 

 tains — opposed to prevailing winds from the ocean receive an abnormal 

 share of the precipitation. But the continental masses themselves are the 

 cause of winds which blow towards them, even in direct reversal of what 

 would, were it not for the existence of the land, be the normal direction of 

 the wind-ciu'rents. The class of winds thus set in motion by the effect of 

 the land masses is known as the monsoon winds. These exist, in fact, almost 

 everywhere along the coasts of the continents, especially in the warmer cli- 

 mates. There is no region, however, where the monsoon winds occur on so 

 grand a scale as on the southern coast of Asia, and esjjecially over Peninsular 

 India. Here, indeed, the system of the trade-winds is entirely reversed 

 during half the ^ear, the effect being that what would otherwise be a bar- 

 ren waste, like by far the greater part of Persia and Arabia, is in most years 



res;ions ; for instance, that of Europe, by Kriinnnel (in tlie Zeitsohiift der Gesellschaft fiir Erdkunde zn Berlin, 

 Vol. XIII.). The contrast in the amount of rain-fall inimeiliately on the coast, and at a little distance from it, 

 in region.s .situated as aljove dcscrilicd, is most remarkahle. Hardly anywhere is it possible to lind a more striking 

 instance of a sadden chanf^e from a moist to a dry climate, than is presented in going up the Columbia Eiver, in 

 Oregon. Within a distance of a few miles one passes from a region exhibiting all the attributes of a richly 

 watered country to one of extreme dryness, the transition being marked by an almost instantaneous change in 

 the wdiole character of the vegetation. Here, of course, it is the Cascade Range which cuts oiT the precipitation 

 from the region to the east of it. 

 * See mite, p. 32. 



