GEOLOGY. 257 



of all the masses of stone so precipitated into the lower 

 lying channel ? In taking this matter into consideration, 

 we are brought upon the consideration of the transporting 

 power of water, which has been previously referred to. 

 The rock, precipitated on to the moving glacier, must 

 move on with the moving mass of ice ; and so within 

 certain limits is it with the sand and gravel borne along 

 by a river. Most are familiar with the appearances pre 

 sented by deposits in a river bed after a flood, which has 

 passed away and left the river bed in many places dry : 

 here shingle, here gravel, here sand. M. Costa de Bastelica, 

 in a work entitled Happort au Conseil Federal sur les 

 Torrents des Alpes Suisses Impedes en 1858-1863, published 

 at Lausanne, gives some information on this subject. He 

 embodies in his idea of a torrent its bearing along earthy 

 matter in suspension ; and he states that it does so both 

 in a mass and in what is known in France as triage, drop- 

 ping some and carrying on others of the materials in 

 question ; in the former case all the rocks, pebbles, and 

 lesser fragments are carried along in something like their 

 relative positions, as would be the case in a viscid mass or 

 in a glacier; in the latter the weightier materials are 

 dropped first, and this going on more or less continuously, 

 the matters in a state of extreme comminution are carried 

 farthest. The difference in mode of transport appears in 

 connection with difference in the velocity of the flow. 

 When this is so great as to bear the whole along in a mass, 

 the stones, whatever their size, do not come into collision, 

 and if any were withdrawn they would be found to be as 

 little rounded as are the stones falling from a glacier, and 

 forming a moraine. 



But when the velocity is being impaired, as this goes on 

 the stones begin to roll, suspended in the water, when they 

 may come into collision one with another ; and the heavier 

 sinking, these are for a time are rolled along the bottom, and 

 subjected to collision and friction. At length they rest, 

 and where they rest the collision of others following and 

 proceeding further subjects them to continued abrasion j 



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