1907. 



AND MOUNTAIN FORMATION. 379 



§ 7. The Effects of Pressure upon the Penetration of Water 

 into the Earth's Crust. — To judge how effective the pressure aris- 

 ing from the depth of the ocean is in driving the water into the 

 crust of the earth, we may observe first that as water is nearly 

 incompressible for moderate pressures, the tendency to penetrate the 

 rocks is everywhere proportional to the depth of the sea. Thus 

 the deeper the water the greater the pressure and penetrating power. 

 Consequently it is chiefly in the deepest water that we should expect 

 to find the maximum effect arising from the secular leakage of the 

 ocean bottoms. In water of any given depth the pressure is theo- 

 retically suflicient to throw a free jet to tlie surface, if the stream 

 could be made to operate in a vacuum. The pressure in a sea one 

 mile deep would thus throw a stream a mile high; in a sea two 

 miles deep, two miles high ; and so on. Now some of the ocean 

 depths exceed five miles, the greatest, near Guam, being 5,269 

 fathoms, almost exactly six miles. Is it therefore any wonder that 

 the deeps east of Japan, near the Aleutian Island, west of South 

 America, near Guam, between Samoa and New Zealand, give rise 

 to enormous leakage of the sea bottom, and consequently many 

 world-shaking earthquakes? A comparatively feeble pressure of 

 water, such as hydraulic engineers use in mining, rapidly cuts away 

 hills and washes out all their gold; in the same way the waters of 

 Niagara, falling through only 160 feet, slowly wear away the solid 

 rock over which they pour.* What then may be expected of a con- 

 stant water pressure which will throw a jet five miles high? Such 

 is the pressure all over the bed of the Tuscarora Deep, and it con- 

 tinues from year to year, century to century. It is this pressure 

 which forces the water so rapidly into the earth, and gives rise 

 to all the great earthquakes and sea waves with which Japan is 

 afflicted. No stone on earth, however thick its layers, could with- 

 stand such a pressure ; nay, under it the water would go through the 

 hardest metals, and sink down deeper and deeper into the bowels 



* This analogy with the hydraulic effects of streams of water in motion is 

 not perfect, for the water in the deep seas is merely subjected to great pres- 

 sure, without bodily movement; yet in both cases the water penetrates the 

 stone to a certain depth. In the one case the water keeps on descending into 

 the earth, in the other the surface particles are carried away by the moving 

 stream. 



