igoS] THE PHYSICS OF THE EARTH. 159 



As the leakage of the oceans seems to be clearly proved by the 

 movements noticed in earthquakes, especially where mountain for- 

 mation is now going on in the depths of the sea, and the seismic 

 disturbances are therefore accompanied by the sinking of the sea 

 bottom, as shown by the seismic sea waves which follow the earth- 

 quakes, it seems legitimate to appeal to these movements of molten 

 matter beneath the earth's crust as the only available means of 

 demonstrating the porosity and other physical properties of layers 

 of granite twenty miles thick. Owing to the restricted conditions of 

 human life, no experiments on such a grand scale can ever be at- 

 tempted in our laboratories, however great the facilities at our 

 command ; and our only means of ascertaining the truth with regard 

 to the theory of ocean leakage is by careful observation in the great 

 laboratory of nature. The leakage of the oceans involves three 

 important questions: (i) The porosity of thick layers of matter 

 such as those composing the earth's crust; (2) the penetrability of 

 the crust under steady fluid pressure, by which the capillary forces 

 are made to aid the molecular forces producing penetration of the 

 fluid; and (3) the accumulation of stresses depending on the forma- 

 tion of steam in the layers just beneath the earth's crust. 



The conditions existing in nature can scarcely be approximated 

 in our laboratories, on account of the limitations of the forces at our 

 command, but so far as experiments throw light on these great 

 questions, the evidence tends to confirm the theory of ocean leakage. 

 The well-known experiments of Daubree, showing that under the 

 action of capillary forces hot water will penetrate a layer of sand- 

 stone against a strong counter pressure of steam, and by entering 

 a cavity actually increase the steam pressure on the further side, has 

 been justly held to afford evidence of the leakage of the earth's 

 crust, and of the probable mode of volcanic activity. If such action 

 is possible in a minute way, it may easily operate on a vastly greater 

 scale to produce the shaking of the crust in earthquakes, together 

 with the uplift of mountains and the occasional outbreak of 

 volcanoes. 



Now if the rock of the earth's crust is at all as porous as we 

 generally think, the constant pressure of the vertical column of 



