August 10, 1906.] 



SCIENCE. 



163 



may bring to bear upon deep-seated and 

 perhaps already heated solid rock masses 

 a sufficient pressure to cause them to re- 

 adjust their positions, and the condition 

 demanded by the theory is present. Such 

 a condition would mean movement of such 

 masses over considerable distances at high 

 pressures, with the final result of the 

 formation of molten streams ready to es- 

 cape upward from the pressure exerted 

 upon them. A vent would at last form 

 and the rush of the partially melted rocks 

 towards and out of this vent would become 

 a lava flow. These actions would naturally 

 occur at places of flexure such as would 

 tend to form a ridge, and the loading and 

 sinking of sea bottoms as a consequence of 

 sedimentary deposits would be favorable, 

 as is well known, to such flexure as would 

 tend to heavily compress the rocks along 

 the line of flexure deep down from the 

 earth's surface, while relieving or not in- 

 creasing pressure near the surface. The 

 compressed rock would in general tend to 

 be shifted or made to flow outward at the 

 line of flexure. This view accords well 

 with the facts. Volcanoes exist along lines 

 more or less parallel to or adjacent to sea 

 coasts or along the weak lines in the earth 's 

 surface. It will easily be seen that a single 

 volcanic vent or pipe may serve to relieve 

 or provide a point for outflow for the shift- 

 ing of material over a great length of 

 flexure deep down under the earth's sur- 

 face. As the flow and fusion would be a 

 somewhat gradual process it may well be 

 that only when the vent is about to open 

 will there be earthquakes and great sub- 

 terranean noises, more or less local to the 

 place of outbreak. Very probably erup- 

 tions in which melted lava does not appear 

 to have a part, but in which steam and 

 gases, sand, or mud are ejected, are never- 

 theless dependent upon an upthrust of lava 

 or a subterranean lava stream, which never 



reaches the surface, but the temperature 

 of which is such that, on its reaching 

 hydrous rock strata, the water is evolved 

 as steam at high pressure, which entering 

 superincumbent layers gives rise to mud 

 eruptions, or escapes from vents or fuma- 

 roles. 



It would be expected that such rock 

 masses as, under pressure, would yield most 

 readily would be the ones to flow and form 

 lavas. They would also be likely to be 

 the more readily fusible masses, assuming 

 that before the process of compression and 

 extrusion begins they exist at a tempera- 

 ture more or less elevated above that at 

 the surface of the earth. The locus of the 

 rock flow might, therefore, be in deep re- 

 gions several miles down, so deep indeed 

 that relief of pressure could not occur by 

 folding of upper layers or strata, which 

 would involve the bodily uplift of rocks 

 above, which rocks, exerting an enormous 

 downward pressure, may be of great rela- 

 tive rigidity. 



The view of the origin of volcanic heat 

 here advanced makes the paroxysmal na- 

 ture of volcanic eruptions almost a neces- 

 sity of the case. The rocks would resist 

 an accumulation of pressure tending to 

 cause them to flow, but finally, under con- 

 tinued increase of force, they would begin 

 to readjust themselves. This would result 

 in heating, softening and fusion. A vent 

 might form and tjius on account of the 

 fluidity of the moving mass the accumulated 

 pressure would for the time be relieved. 

 But the original causes might still exist 

 and continue, even after cooling of the 

 heated material in the vents, to result in 

 pressure accumulation, renewed flow and 

 fresh outbreaks at periods more or less re- 

 mote. The final decay of volcanic action 

 in any region would result from such a 

 permanent readjustment of strains as to 

 entirely relieve the rock masses of any pres- 



