REMOVAL OF ROCKS AND GRAVEL BY STREAMS. 485 



as in mountain torrents, or other places where numerous 

 rapids occur: very little small stuff is ever seen in the 

 dry channels of such streams; but water which flows 

 with much less velocity is still capable of moving the 

 smaller sizes of such stones, for it must be borne in 

 mind that the weight of objects, such as stones, etc., 

 becomes considerably less in water than they are when 

 out of it, because of the much greater density of water 

 than of air. The supporting power of water is there- 

 fore infinitely greater, as the swimmer finds when he 

 maintains himself afloat upon its surface, much as a 

 bird does in the air. According to Professor Huxley, 

 " if a stone be twice as heavy as an equal bulk of 

 water, it will lose half its weight when immersed in 

 it. If three times as heavy, one third; if four times 

 as heavy, one fourth, and so on." * Then as regards 

 the actual power of streams in transporting such 

 objects from place to place, Professor Huxley lends 

 the weight of his authority to the statement, that a 

 stream flowing at the rate of 36 inches per second 

 {= 3600 yards an hour, 3520 yards being two miles), 

 " can transport pebbles as large as hen's eggs ; " " if 

 at 12 inches per second, it can sweep away fine 

 gravel, " f and " at the rate of 6 inches per second " 

 (= 600 yards per hour), "it has power to carry off 

 fine sand." Of course, with very little current, a 

 stream can still bear along mud, and other matters 

 mingled with its waters in a state of semi-solution. 



* Physiography, by Professor Huxley, F.R.S., 1887, p. 133. 



7 Ibid., p. 133. No doubt the professor here means to indicate 

 that pebbles of this size are moveable merely by a stream running 

 at this rate, and are thus rolled slowly onward by it. 



Ibid., p. 133. 



