MOVNTAINS AND CIA MATE. Monntains fulfill important uses. in the economy of nature, espe cially in connection with the water system of the world. They are at once the great collectors and distributors of water. in the passage of moisture-charged winds across them. the mois ture is precipitated as rain or snow. When mountain range's intersect (.1/11",1' of constant and abstract the moisture, they produce a moist country on the windward side. and a eomparatively dry and arid one on the leeward.
This is exemplified in the Andes, the precipitous western surface of which lens a different aspect from the sloping eastern plain; and so also the greater supply of moisture 00 the southern side's of the Himalayas brings the snow-line :i0O0 feet lower than on the northern side. Above a certain height the moisture falls as snow, and a range of snow-clad summits would form a more effee• tual separation between the plains on either side than would the widest ocean, were it not that transverse valleys are mf frequent occurrence.
which open up a pass, or way of transit. at a level below the snow-line. Rut even these would not prevent the range being an impassable bar rier if the temperate regions contained as 14 thy mountains as the tropics. fountains also show considerable vertical variation in their life and elimate zones. It is well known that, other things being equal. the air is one degree cooler for every 300 feet of ascent, and also that the rate of pre cipitation inerea,CA upward. At. a certain eleva tion rain gives way tee snow. Corresponding to these varying conditions of temperature and moisture is the Ilistribution of the vegetation, whirl is commonly in well•defined zones. each zone distinguished by its species from the zones alcove and below. Near the top of many moun tains the vegetation ends altogether. and the top of the' mountain is barren.