(6) Moseley assigned the movement to a bodily expansion and contraction of the glacier, analogous to the creeping of a mass of lead on a roof; (7) James Thompson demonstrated that pressure lowers the melting-point, and while this effect is so small as probably to be ineffectual, it is correlated with the very important fact that compression may cause melting, which is not the case in most other rocks. He recognized that under pressure partial liquefaction took place, that the water so liberated might be refrozen as it escaped from pressure, and appears to have regarded this as a vital factor; (8) Croll held that the movement was due to a consecutive series of molecular changes somewhat like the chain of chemical combinations in electrolysis; (9) Hugi, Eli de Beaumont, Bertin, Forel, and others thought that the growth of the granules was the leading factor in the ice movement; (10) McConnel and Mügge have made the gliding planes of the ice crystals serve an important function in glacial movement. It will be seen that the principle of partial liquefaction for which Thompson laid the basis, the crystallization of descending water, urged by Charpentier and Agassiz, and the granular growth on which Hugi, Beaumont, Forel, and others founded their hypotheses, are incorporated in the view already presented. Probably the agencies on which some of the other views are based may also be participants in producing glacial motion, sometimes as incidental factors, and sometimes perhaps as important ones, for under different conditions, different agencies may play rôles of varying importance. For example, in going over the brinks of precipices of sufficient height, glaciers break into fragments which are re-cemented below, and the “reconstructed” glacier moves on as before. Here fracture and regelation are evident. The movement of the gliding planes of the ice crystals over each other, which has been looked upon as a special kind of viscoid movement, probably plays a large part in the shearing movements in certain cases. But neither of these is probably a large factor in ordinary glacial movement, and it seems highly improbable that any of them are essential factors in the primary movements in the snow-fields where glacial action begins. CHAPTER VI. THE WORK OF THE OCEAN. The general facts concerning the depth of the ocean and the distribution of its water have been given on a preceding page (p. 8), and the origin of the ocean and the ocean basins is discussed in the second volume. This chapter has to do primarily with the processes now going on in the sea and its borders, in so far as they are of importance in the interpretation of geologic history. The study of these processes is prefaced by a few words concerning the amount and composition of the sea-water, the life of the ocean, and the topography of its bed.[138]