322 THE PHYSICAL GEOGRAPHY OF THE SEA. 



solid rock. But what are the Hudson and the Niagara, with all 

 the fresh water-courses of the world, by the side of the Gulf 

 Stream and other great " rivers in the ocean ?" And what is the 

 pressure of fresh water upon river-beds in comparison with the 

 pressure of ocean water upon the bottom of the deep sea? It is 

 not so great by contrast as the gutters in the streets are to the 

 cataract. Then why have not the currents of the sea worn its 

 bottom away? Simply because they are not permitted to get 

 down to it. Suppose the currents which we see at and near the 

 surface of the ocean were permitted to extend all the way to the 

 bottom in deep as well as shallow water, let us see what the press- 

 ure and scouring force would be where the sea is only 3000 

 fathoms deep — for in many places the depth is even greater than 

 that. It is equal there, in round numbers, to the pressure of six 

 hundred atmospheres. Six hundred atmospheres, piled up one 

 above the other, would press upon every square foot of solid mat- 

 ter beneath the pile with the weight of 1,296,000 pounds, or 648 

 tons. 



597. The better to comprehend the amount of such a pressure. 

 Their pressure on ^^^ ^"^^ imagine a columu of water just one foot 

 the bottom. square, where the sea is 3000 fathoms deep, to be 



frozen from the top to the bottom, and that we could then, with 

 the aid of some mighty magician, haul this shaft of ice up, and 

 stand it on one end for inspection and examination. It would be 

 18,000 feet high ; the pressure on its pedestal would be more than 

 a million and a quarter of pounds ; and if placed on a ship of 648 

 tons burden, it would be heavy enough to sink her. There are 

 currents in the sea where it is 3000 fathoms deep, and some of 

 them — as the Gulf Stream — run with a velocity of four miles an 

 hour, and even more. Every square foot of the earth's crust at 

 the bottom of a four-knot current 3000 fathoms deep would have 

 no less than 506,880 — in round numbers, half a million — of such 

 columns of water daily dragging, and rubbing, and scouring, and 

 chafing over it, under a continuous pressure of 648 tons. What 

 would the bottom of the sea have to be made of to withstand such 

 erosion ? Water running with such a velocity, and with the fric- 

 tion upon the bottom which such a pressure would create, would 

 in time wear away the thickest bed, though made of the hardest 

 adamant. Wh}^, then, has not the bottom of the sea been worn 



