I907.] AND CONTRACTION OF THE EARTH. 285 



17. At one time or another the principal oceans form mountains 

 all around them, but in any one geological age the relief may be 

 chiefly on one side, except when the ocean is of very great extent, 

 like the Pacific,^ which therefore is active all around, and obtains 

 some internal relief by the formation of numerous islands. 



18. We have shown that just as soon as the exploding lava 

 acquires sufficient tension or elastic pressure to lift the crust along 

 a fault line, a displacement occurs there, and the lava spreads beneath 

 the block thus moved, giving relief along the path of least resistance. 

 It is the enforced movement of these subterranean lava streams which 

 shakes down cities and devastates whole countries. 



19. It is found that secular cooling is so very slow and so small 

 in amount that it has no sensible effect on the physics of the globe. 

 Accordingly it is shown that the earth is not now shrinking, nor has 

 it been at any time since the consolidation began. 



20. On the contrary the formation of pumice everywhere beneath 

 the land, as it is elevated by the steam forming under the oceans, is 

 raising the level of the continents, in spite of erosion. And as the 

 oceans are being gradually narrowed by the recession of the sea, after 

 successive mountain chains are formed — some of the water sinking 

 beneath the earth's crust, and the rest collecting into a smaller area, 

 here and there growing deeper when lava is expelled from beneath 

 the margins — it may well be that the ocean level is nearly stationary, 

 or rising slightly with respect to the centre of the earth, though there 

 is a secular lowering of the strand line relatively to the land. Ac- 

 cordingly so far from contracting the earth may be in reality very 

 slightly expanding. This secular expansion is due to the formation 

 of pumice nearly everywhere beneath the crust. 



* In his Manual of Geology, 1863, the late Professor J. D, Dana came 

 surprisingly near many of the views reached in the present investigation. 

 He pointed out with great clearness that the continents not only are built 

 on one model, with the mountains around their borders, while the interior 

 is a depressed basin, but also that the highest border is on the side of the 

 greatest ocean, and conversely. In speaking of this fundamental law he re- 

 marks that " the relation between the extent of the oceans and the height 

 and volcanic action, etc., of their borders proves that the amount of force 

 in action had some relation to the size and depth of the ocean basin. The 

 Pacific exhibits its greatness in the lofty mountains and volcanoes which 

 begirt it." 



