CUERENTS OF THE SEA. 183 



rison witli the rate it assumes as it approaches the Falls ; and it is 

 sluggish in deep places, rapid in shallow ones, because it is fed from 

 below. The common " wastes " in our canals teach us this fact. 



388. The reasoning of this celebrated geologist appears to be 

 The bars at the fouudcd upou the assumptiou that when water, in 

 Sppi^iuusua-* consequence of its specific gravity, once sinks below 

 *i"^"- the bottom of a current where it is shallowest, there 



is no force of traction, so to speak, in fluids, nor any other power, 

 which can draw this heavy water up again. If such were the case, 

 we could not have deep water immediately inside of the bars which 

 obstruct the passage of the great rivers into the sea : the bar at the 

 mouth of the Mississippi, with only fifteen feet of water on it, is 

 estimated to travel out to sea at rates varying from twenty to one 

 hundred yards a year. In the place where that bar was when it 

 was one thousand yards nearer to New Orleans] than it now is, 

 whether it were fifteen years ago or a century ago, with only fif- 

 teen or sixteen feet of water on it, we have now four or five times 

 that depth. As new bars were successively formed seaward fi-om 

 the old, what dug up the sediment which formed the old, and hfted 

 it up fi'om where specific gravity had placed it, and carried it out to 

 sea over a barrier not more than a few feet fi^om the surface ? In- 

 deed, Sir Charles himself makes this majestic stream to tear up its 

 own bottom to depths far below the top of the bar at its mouth. 

 He describes the Mississippi as a river having nearly a uniform 

 breadth to the distance of two thousand miles from the sea.* He 

 makes it cut a bed for itself out of the soil, which is heavier than 

 Admiral Smyth's deep sea water, to the depth of more than two 

 hundred feet t below the top of the bar which obstructs its entrance 

 into the sea. Could not the same power which scoops out this 

 solid matter for the Mississippi draw the brine up from the pool 

 in the Mediterranean, and pass it out across th^ barrier in the 

 Straits ? The currents which run over the bars and shoals in our 

 rivers are fed from the pools above with water which we know 

 comes firom depths far below the top of such bars. The breadth 

 of the river where the bar is may be the same as its breadth where 

 the deep pool is, yet the current in the pool may be so sluggish as 



* " From near its mouth at the Belize, a steam-boat may ascend for two thou- 

 sand miles with scarcely any perceptible difference in the width of the river." — 

 Lyell, p. 263. 



t " The Mississippi is continually shifting its course in the great alluvial plain, 

 cutting frequently to the depth, of one hundred, and even sometimes to the depth 

 of two hundred and fifty ieet"— Lyell, p. 273. 



