286 HOBBS— THE EVOLUTION AND THE [April 24, 



ing our knowledge of surface displacements of the earth to the floor 

 of the oceans, it has brought us a surprise ; for we have learned that 

 to these areas, by many regarded as so stable, belong a much larger 

 proportion of the grander movements, and by presumption of the 

 smaller ones as well. The recent study of the ocean floor through 

 soundings, examined with reference to the loci of suboceanic quakes, 

 has told us, further, that though the movements upon the land are 

 generally upward, those upon the ocean bottom, on the contrary, are 

 downward. The so-called *' origins " of the oceanic quakings are 

 most frequently the steep borders of the great sea troughs where the 

 greatest depths have been revealed by soundings. Now it is as impos- 

 sible to separate the idea of molar displacements from these great 

 disturbances as it is to avoid the conclusion that since these troughs 

 are now the deepest bottoms, this is a direct consequence of the 

 repeated displacements which must accompany the quakings. It 

 has, moreover, been a general result of direct observation, that with 

 noteworthy local exceptions the sea-coasts are to-day undergoing 

 elevation, and that the steeper coasts face the greater depths.*" 



It is difficult to avoid the conclusion that the general upward 

 movement of the margins of the continental areas and the general 

 downward movements of the near-lying oceanic floors are inter- 

 related as parts of one general adjustment within the outer shell of 

 our planet. This granted, there is no difficulty in conceiving of the 

 rise of block mountains upon the continental borders, since the 

 increase of superficies within the affected continental region is com- 

 pensated by a contraction of area in portions of the sea floor which 

 in the same general period are subsiding. A rise of block moun- 

 tains to the accompaniment of an earthquake, if our theory of cause 

 be correct, though it calls for an expansion of the surface, should 

 reduce the superficies of the affected region if measured on the sur- 

 face of a sphere at its former level. A renewed and sudden com- 

 pression of the district is thus made possible through the action of 

 the tangential compressive stresses within the contracting shell. 

 The writer believes that evidence of such compression has been 



'" See, among others, G. Schott u. P. Perlewitz, " Lothungen I. N. M. S. 

 " Edi " und des Kabeldampfers " Stephan " im westlichen Stillen Ozean," 

 Arch. d. deutsch Seczvarte, Vol. 29, 1906, pp. 5-1 1. 



