202 THE PEAKS AND MOUNTAIN RANGES
subsequently carved by the process of erosion into clusters of peaks. The great peaks being thus of intrusive origin, the question naturally arises whether they are still being intruded upward ; whether those great forces at work beneath the surface of the earth are still impelling them upward; and if so, whether they are being forced upward more rapidly than the atmospheric forces are wearing down their summits. From the geological standpoint Mr. Hayden says that it is not at present possible to say whether the elevatory movement is still in progress, but he adds that many phenomena observable in the Himalaya lead us to infer that local elevation has until quite recently been operative, and the numerous earth- quakes still occurring with such frequency and violence forcibly remind us that the Himalaya has by no means reached a period of even com- parative rest. The surveyor can as yet give us no more certain answer. Colonel Burrard says the original observations of the great peaks made between 1850 and 1860 were not sufficiently pro- longed at any one station to enable us to rely with certainty on the values of the height then obtained. When a slow variation in height has to be deter- mined it is better to carry out a long series of
