1883.J 475 [Crosby. 



reversed to the extent of a few thousand feet, but never sufficiently 

 to convert the sea-bottom into dry land. Yet this cold, thick, 

 stable oceanic crust, which has never been weakened by thick sed- 

 imentary deposits, is an area of wide spread and intense volcanic 

 activity ; while the continental interiors which, according to the 

 theory in question, have experienced far greater oscillations of 

 level and are covered by unknown but great thicknesses of strat- 

 ified rocks, are almost entirely free from active volcanoes. 



Volcanoes have burned, and poured out their floods of rock, 

 over nearly all parts of the continents. But all volcanoes are, in 

 a geological sense, short lived; and, ere the sediments through 

 which they reach the surface have become old, their energy is 

 exhausted and the wound in the earth's crust is permanently 

 healed. And there can be little doubt that active, terrestrial 

 volcanoes follow the sea-shore simply because it is there, chiefly, 

 that thick deposits of recent sediments are found. It is a natural 

 inference from these considerations that the volcanoes of Polyne- 

 sia, for example, are piled upon thick sedimentary formations 

 deposited, perhaps, during the slow subsidence of a great Pacific 

 continent. But, according to Professor Dana, they are quite un- 

 like terrestrial volcanoes, having no necessary connection with 

 sediments and being as old as the earth's crust. 



The submarine mountain-ranges are, equally with the oceanic 

 volcanoes, an argument against the immutability of oceanic con- 

 ditions. Few geological theories are now more generally accepted 

 than the theory that mountains are formed by the horizontal 

 mashing up of thick deposits of sediments. These stratified form- 

 ations of immense thickness — five to ten miles for most impor- 

 tant mountain-systems — can only be formed on a marginal sea- 

 bottom. Hence it is impossible to avoid the conclusion that 

 mountains are of sea-shore origin. But an application of this 

 theory to the submarine mountain-ranges is fatal to the notion 

 that the oceanic abysses are permanent. Yet what warrant have 

 we for supposing that these grand corrugations of the ocean-floor 

 are different in structure and origin from the continental moun- 

 tain-systems ? The supposition that they are composed entirely 

 of volcanic ejectamenta is contrary to all analogy and extremely 

 improbable. No well defined and important mountain-ranges on 

 the land have this composition. While the idea that submarine 



