SUBMARINE MOUNTAINS 57 



cooling is affected by the furnace-heat of chemical reactions. 

 It is, indeed, uncertain that the initial temperature of the 

 emanating gas was below that of white heat. If it were so 

 high, the rock at the deep level of origin could not be truly 

 solid, that is, crystallized; it would have been largely or wholly 

 in the glassy state. 



Other volcanologists favor the view that the source of the 

 live lava at any volcanic center is a local reservoir of molten, 

 gas-charged rock in the otherwise crystallized earth. This sec- 

 ond hypothesis has been proposed to account for the distribu- 

 tion of the various chemical species represented by volcanic 

 rocks, and also to reconcile the presence of liquid rock in a 

 planet which, in average, is more "rigid" than steel. Neither of 

 these arguments for assuming that all lava emanates from 

 localized subterranean reservoirs is valid, and the hypothesis 

 suffers from the lack of any adequate cause for the localization 

 of melting in depth. 



Less troublesome is a third suggestion — that, during most 

 of geological time, both land and ocean volcanoes were fed 

 from a continuous, world-circling layer of red-hot to white-hot 

 material, beginning at a depth no greater than about 50 miles. 

 It is now assumed that the temperature of this level was high 

 enough to produce a glassy, vitreous state, even at the high 

 pressure ruling at and below the depth of 50 miles. This third 

 explanation for the elevated temperature of erupted matter is 

 based on the study of volcanology in the broadest sense. The 

 reader will note that the general conception of strong crust and 

 hot, glassy, weak substratum was reached when, in Chapter I, 

 the physics of the general sea floor was studied. 



A principal fact from which the preferred hypothesis has 

 been derived is the dominance of the dark-colored, relatively 

 dense lava bearing the familiar name of basalt. On land and 

 sea floor alike, in overwhelming floods, this primary molten 



