1883.] 473 [Crosby. 



Now suppose that after a submergence of ten million years the 

 floor of the deep ocean is slowly raised to form dry land. Is it 

 surprising that a bed five or possibly ten feet thick of ferrugin- 

 ous clay containing organic remains similar to those found in 

 shore deposits is not recognized as of abyssal origin, but is com- 

 pletely lost among the miles of marginal sediments composing 

 the new continent? In the ordinary sense there are no abyssal 

 sediments, but we find over these oceanic wastes merely the im- 

 palpable dust that slowly settles during the lapse of countless 

 ages from the limpid water of the central sea. The land is the 

 great theatre of erosion and the sea of deposition; but just as 

 there are extensive rainless tracts on the continents where there 

 is practically no erosion so there exist still larger areas of the 

 ocean-floor over which the complementary process, or deposition, 

 approaches the vanishing point. On both land and sea the main 

 field of geological operations is marginal, following the shore 

 line; but nowhere does the earth's crust experience such perfect 

 rest as under the deep sea. 



A large proportion of the volcanoes of the globe are in the 

 central portions of the ocean, nearly all the oceanic islands being 

 either volcanic, or consisting of coral-rock resting upon old sub- 

 merged volcanoes ; while of the submarine volcanoes which have 

 never reached the surface we of course know nothing, but it is 

 probable that such exist and possible that they out-number those 

 whose craters are dry land. Now on the land we observe no im- 

 portant exception to the rule that volcanoes are situated upon, 

 or in the immediate neighborhood of, thick deposits of recent 

 sediments — Tertiary or Secondary. And we also observe that 

 in the earlier periods of the earth's history the same law held 

 good. 



Are the oceanic volcanoes to be regarded as exceptions to this 

 general law? If so, upon what ground? If not, then the infer- 

 ence is at least probable that the great volcanic archipelago of 

 the Pacific, as well as the numerous volcanic islands in the 

 Atlantic and Indian Oceans, rests upon extensive stratified forma- 

 tions of no great geological age. But the deep sea sediments, as 

 we have seen, are of very trifling thickness, with the exception of 

 the coral-limestone ; and this rests upon, and is newer than, the 

 volcanoes. Hence the inference is plain that the floor of the 



