Of what are these great peaks built up? No one has yet ascended their summits, and as Mr. Hayden points out, the geologist has to do his work at close quarters, and not like the surveyor from a distance. So the composition of the highest peaks is rarely known in any detail, though the general character of the rocks can be ascertained with a fair approximation to certainty, from observation of material on the flanks, and from a distant view of the weathering character and apparent structure of the peaks themselves. From such observations it has been found that almost all the peaks of 25,000 feet or more in height are composed of granite, gneiss, and associated crystalline rocks. It had long be supposed that some of the granites found on the flanks of the great peaks which presented a foliated appearance were of sedimentary origin, and had therefore been once deposited beneath the sea. But their truly intrusive nature was recognised by the late Lieutenant-General M'Mahon, who proved conclusively that the great central gneissose rock of the Himalayas was in reality a granite crushed and foliated by pressure. It may certainly be taken that both K2 and Nanga Parbat are composed of granite, and have been intruded or compressed upward from beneath the earth's crust.
Mr. Hayden further concludes that the exceptional height of these great peaks is due to their being composed of granite, for either the superior power of the granite to resist the atmospheric forces tending to their degradation has caused them to stand as isolated masses above surrounding areas of more easily eroded rocks, or they are areas of special elevation.
[Illustration: LAKE SHISHA NAG, LIDAR VALLEY]
Now it is found that the axes of the great mountain ranges are also composed of granite, and it seems probable that special elevating forces have been at work to raise certain parts of their ranges above the general level of the whole. And when once such elevation has been brought about, the disparity between the higher peaks and the intervening less elevated area would undoubtedly be intensified by the destructive forces at work, for the mantle of snow and ice, while slowly carrying on its work of abrasion, would serve as a protection for the peaks against the disintegrating forces of the atmosphere, while the lower unprotected areas would be more rapidly eroded.