1906 



SEE— THE CAUSE OF EARTHQUAKES. 289 



To make a practical application of these principles, what shall 

 we now say with respect to the ocean bottoms? In deep places 

 the pressure of the sea water upon them is very great, sufficient 

 to force the water through walls of solid glass several centimeters 

 thick in a short time, and the bed itself in general no tighter than 

 that of a pond in a common field. Obviously, most of these bot- 

 toms will leak, and leak at a rapid rate under the enormous pres- 

 sure operating in the greatest depths of the sea. The bed of 

 the ocean will not leak with equal rapidity in all places, but almost 

 universal leakage will certainly develop ; and the water will be 

 driven down into the earth at various rates depending upon the 

 fluid pressure and temperature and the physical character of the 

 sea bottom. Where the rock is volcanic, and badly fractured, or 

 sandy, the leakage will be most rapid, and where the bed is made of 

 fine clay or unbroken granite, the leakage will be much more 

 gradual. It will also depend directly on the depth of the sea, being a 

 maximum where the ocean is deepest, and generally quite insig- 

 nificant in shallow water. The amount of water leaking through 

 any square meter of the sea bottom will be given by an expression 



of the form 



w = P.p.f(t).<t>(T), 



where P is the fluid pressure in the bed of the sea, and thus directly 

 proportional to the depth ; p the average porosity of the ocean bot- 

 tom, and thus depending on the kind of ooze, dust, sediment and 

 rocks underlying the sea and their state of compression; and f(t) 

 is some function of the time, depending on the average rate of 

 leakage through the successive strata; and cf>(T) is a function 

 of the temperature, and thus increasing with the descent into the 

 rocks of the earth's crust. As water is almost incompressible for 

 small or moderate forces, its escape downward would depend upon 

 the continued descent of that which first entered the bed of the 

 ocean, the rate of which would be diminished under the increasing 

 pressure and density encountered in the lower strata, but on the 

 other hand increased by the rising temperature which makes the 

 rocks more penetrable and also augments their power of absorption. 

 Various values of these quantities, P, p, f(f), <I>{T), would give the 



