The portion of the Southern Himálaya between Great Tibet and India consists of a stupendous chain of snow-clad mountains, with a line of culminating peaks, and slopes deeply furrowed into alternate ravines and ridges, which gradually sink down into the valleys of the Ganges and Brahmaputra. The distance from the culminating ridge to the plain averages about ninety miles; a breadth which Mr. Brian Hodgson describes by dividing it into three equal longitudinal zones: the lower comprising the Dhúns, or Maris of Nepal, and the Dúars ot Bhutan, as well as the bhabur or sal forest, and the terai;[1] the middle, between the Dhúns and the snow line; and the upper or alpine gone. The first ranges from the plains to 4000 feet; the central, from 4000 feet to 10,000 feet; and the upper, from 10,000 feet to 29,000 feet above the sea level. The amount of heat and cold in these several zones depends almost entirely on the elevation, there being a diminution of temperature equal to 3° or 3½° Fahr. for every thousand feet of height. But, as regards moisture, every movement to the west or north-west brings the traveller into a drier climate, and takes him farther and farther from the line of the rainy monsoon, The ridges also, being in the direct line of the monsoon, check its progress, and their height has an effect on the amount of moisture in adjacent valleys. Thus there are great differences of climate in places of equal elevation. The character of the Himálayan slope is a perpetual succession of vast ridges with narrow intervening glens; and open valleys, such as that of Nepal, are very rare.[2]
In ascending the gorges from the terai to the alpine ridges, the traveller passes through three zones of vegetation. In the lower region he finds splendid timber trees, such as the sal and sissu, banyans and peepuls, bamboos and palms. The central slopes are clothed with oaks, chestnuts, magnolias,
