Between these mountain peaks is an almost continuous succession of snow fields and glaciers beyond all comparison. The snow line is 17,000 feet in midsummer, and in winter comes down to 12,000 and 15,000 feet, and when that altitude is reached snow is continuous and impassable. This is the highest and the most extensive of all mountain ranges. Along the northern frontier of India for 2,000 miles it stands like a vast hedge, the most formidable natural boundary in the world, nowhere lower than 17,000 feet, and impassable for armies the entire distance, with the exception of two gateways: Jeylup Pass here and at the Khyber Pass of which I told you in a previous chapter. There are passes over the snow, but their elevation is seldom less than 16,000 feet; the average elevation of the watershed exceeds 18,000 feet, and the great plateau of Thibet, which lies upon the other side, is between 15,000 and 16,000 feet above the sea. This plateau, which is sometimes called the "Roof of the World," is 700 miles long and 500 miles wide, and could not be crossed by an army not only because of the winds and the cold, but also because there is very little water, no fuel and no supplies. No invading force could possibly enter India from the north if these passes were defended, because the inhospitable climate of Thibet would not sustain an army, and the enormous distance and altitude would make the transportation of supplies for any considerable force practically impossible. During the summer the plateau is covered with flocks and herds, but when the cold weather comes on the shepherds drive them into the foothills, where they find shelter. The width of the main range of the Himalayas will average about 500 miles between its northern and southern foot-hills; it embraces every possible kind of climate, vegetation and natural products, and is a vast reservoir from which four of the greatest rivers of the world flow across the plains of India, carrying the drainage from the melting snows, and without this reservoir northern India would be a hopeless and dreary desert. There is a lively dispute among geographers, topographers and other learned pundits of the scientific bureaus of the Indian government as to whether Everest is really the king of the mountains. Other peaks in the group have their advocates, and over in Cashmere are several which lift their heads nearly as high as 30,000 feet, but few of them have been accurately measured, and the height of none can be determined with exactness. Mount Godwin, in Cashmere, is very near the height of Everest, and many claim that Kinchinjunga is even higher.