1909.] OUTLOOK OF SEISMIC GEOLOGY. 275 



is only beginning to be appreciated. Fortunately this hypothesis 

 may be fitted to the now quite generally accepted view that the 

 earth is essentially solid throughout, and is maintained in that condi- 

 tion at great depths below the surface by the high pressure from the 

 superincumbent material. Now the arching of strata in the process 

 of folding is competent to lift the load from underlying rocks, so 

 that wherever their temperature is such that fusion would occur at 

 the surface, a reservoir of molten lava is produced and will be 

 brought to the surface from the action of gravity whenever a path 

 is open for it. A reason is thus found for the presence of lava 

 bodies at moderate distances only from the surface in those districts 

 where the process of mountain building is in operation. 



The Mesh-like Distribution of Volcanic Vents. — The lineal 

 arrangements of volcanoes and the dependence of this alignment 

 upon the existence of fissures through the crust, seems to have 

 been one of the earliest of geological observations, so soon as the 

 less civilized continents had been scientifically explored. In Europe 

 the systematic arrangement of volcanoes is much less strikingly dis- 

 played, and it was there in consequence a later discovery. The 

 credit for having first recognized this important fact of observation 

 is generally given to von Buch, because of his classical study of the 

 Canary Islands. It seems probable, however, that Alexander von 

 Humboldt, his friend and colleague in the field of geological ex- 

 ploration, was the first to make the observation. The latter showed 

 that the volcanoes in the Cordilleran system of South and Central 

 America furnish striking examples of such alignment. Von Buch, 

 in his turn, emphasized this significant relationship, but found cer- 

 tain volcanic districts within which the alignment of vents was not 

 apparent, and so he distinguished volcanic chadns from central 

 volcanoes. Other explorers like Dana and Darwin soon added con- 

 firmation of a linear arrangement from the regions which they had 

 individually visited. Dana, a member of the Wilkes Exploring Ex- 

 pedition, brought out the lineal arrangement of the Polynesian 

 Islands and showed that all these were alike rows of partly sub- 

 merged volcanic peaks. ^° Darwin, during his voyage on the 



^ " Manual of Geology," pp. 37, 282. 



