THE BASIN AND BED OF THE ATLANTIC, ' 309 



596. The tooth of running water is very sharp. See how the 

 The abrasion of Hudson has gnawod through the Highlands, and the 

 currents. Niagara cut its way through layer after layer of the 



sohd 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 pres- 

 sure 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 sm-face 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 pressm-e 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 sohd matter 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 let US imagine a column of water just one foot 

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



frozen fi'om 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 pressm-e on its pedestal would be more than 

 a miUion 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 

 cm-rents 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 rubbmg, 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 

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

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

 adamant. Why, then, has not the bottom of the sea been worn away ? 



