350 CLIMATE DEPENDENT ON THE 



may have often occurred, and, involving cataclysms, 

 swept tlie surface to produce the changes we detect over 

 every part of the earth, compared with which the earth- 

 quakes and floods of history are but trivial things. 

 Evidence has been adduced, to show that the mountains 

 of the Old World may have approached in height the 

 highest of the Andes or Himalayas, and these have not 

 been destroyed by any sudden effect, but by the slow 

 disintegrating action of the elements.* All these 

 phenomena are now in progress : the winds and the 

 rains wear the faces of the exposed rock ; their debris, 

 mixed with decayed vegetable and animal matter, are 

 washed off from the surface, and borne away by the 

 rivers, to be deposited in the seas. Thus it is that the 

 great delta of the Ganges is formed, and that a continual 

 increase of matter is going on at the mouths of rivers. 

 The Amazon, the Mississippi, and other great rivers, 

 bear into the ocean, daily, thousands of tons of matter 

 from the surface of the earth. f This is, of course, de- 



-'' See Professor Ramsay's memoir On Denudation: Memoirs 

 of the Geological Survey of Great Britain. 



f " The distances to which river water, more or less charged 

 with detritus, would flow over sea water, will depend upon a variety 

 of obvious circumstances. Captain Sabine found discoloured water, 

 supposed to be that of the Amazons, three hundred miles distant 

 in the ocean from the embouchure of that river. It was about 

 126 feet deep. Its specific gravity was = r0204, and the specific- 

 gravity of the sea-water = 1-0262. This appears to be the 

 greatest distance from land at which river water has been detected 

 011 the surface of the ocean. If rivers, containing mechanically 

 suspended detritus, flowed over sea-water in lines which, in general 

 terms, might be called straight, the deposit of transported matter 

 which they carried out would also be in straight lines. If, 

 however, they be turned aside by an ocean current, as was the 

 case with that observed by Captain Sabine, the detritus would be 

 thrown, and cover an area corresponding in a great degree with 

 the sweep which the river has been compelled to make out of the 

 course, that its impulse, when discharged from its embouchure, 

 might lead it to take : supposing the velocity with which this rivc-r- 

 water was moving has been correctly estimated at about thrci- 



