186 THE PHYSICAL GEOGRAPHY OF THE SEA. 



is at the Falls, we should have a current as rapid as it is at the 

 moment of passing the top of the rock to make the leap. To see 

 that such is not the way of Nature, we have but to look at any 

 common mill-pond when the water is running over the dam. The 

 current in the pond that feeds the overflow is scarcely perceptible, 

 for " still water runs deep." Moreover, we know it is not such a 

 skimming current as the geologist would make, which runs from 

 one lake to another; for wherever above the Niagara Falls the 

 water is deep, there we are sure to find the current sluggish, in 

 comparison with 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. 



888. The reasoning of this celebrated geologist appears to be 

 Ti.e bars at the fo^udcd upou the assumptiou that when water, in 

 Sippi an uTusTra- consequcncc of its specific gravity, once sinks below 

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



is no force of traction^ so to speak, in fluids, nor any other pow- 

 er, 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. Thus 

 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 

 one hundred to twenty 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 fifteen or sixteen feet of water on it, we have now four or 

 five times that depth. As new bars were successively formed 

 seaward from the old, what dug up the sediment which formed 

 the old, and lifted it up from where specific gravity had placed it, 

 and carried it out to sea over a barrier not more than a few feet 

 i';om the surface? Indeed, Sir Charles himself makes this majes- 

 tic 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 



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

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

 p. 2G3. 



