280 K. T. HILL — PELE AND THE WINDWARD ARCHIPELAGO 



maintain that predetermined fissures are essential for volcanic extrusion 

 and inletting of water, and all crustalists postulate that the water of erup- 

 tions is derived from crustal sources. 



Mallet maintained that all the present manifestations of hypogene 

 action are due directly to the more rapid contraction of the hotter in- 

 ternal mass of the earth and the consequent crushing in of the outer 

 cooler shell. " The secular cooling of the globe," he remarked, " is always 

 going on, though in a very slowly descending ratio. Contraction is there- 

 fore constantly providing a store of energy to be expanded in crushing 

 parts of" the crust, and through that providing for the volcanic heat." 

 Professor N. S. Shaler has also advanced a crustal " blanketing theory," 

 in which he accounts for the volcanic heat by continuous accretions of 

 sediments or load. 



The theory of the " fissurists," who maintain that volcanic action itself 

 is due to the letting in of water through fissures to the hot magma, has 

 been expressed by Dana, who states : * 



" For expansive eruptions, water in large quantities must gain sudden access to 

 the interior of a magma conduit, for the projectile force of the abruptly generated 

 vapors is enormous." 



Russell,t in his excellent work on North American volcanoes, while 

 admitting that the initial expansion of the magma forced it up into the 

 subterranean fissures of the crust, postulated that the actual eruptions 

 at the surface required the inletting of surface waters. 



An exposition of the crustal theory, in its extreme development and 

 application to the West Indian eruption, was recently set forth by Pro- 

 fessor Milne in the Journal of the Royal Geographical Society of London 

 for January, 1903. 



Briefly stated, Milne's theory is that dormant volcanoes in a state of 

 volcanic strain may be brought into activity by a mass displacement of 

 a fold from which they rise. This displacement may occur a thousand 

 miles or more from the site of the volcano. For instance, he alleges that 

 the eruption of mont Pele in 1851 was preceded by a great earthquake 

 in Chile, fully 2,000 miles distant. 



According to this author (but not so in nature), nearly all active vol- 

 canoes occur along the ridges of rock folds which are in proximity to 

 oceanic waters. By the percolation of this water to the foundations of 

 these folds, where it comes in contact with a heated magma, extraordi- 

 nary pressures are developed, the sudden relief of which results in a vol- 

 canic outburst. 



♦ The term "magma" is used by geologists for the molten igneous volcanic fluid which differ- 

 entiates into various kinds and forms of crystalline rock under physical conditions of pressure, 

 cooling, etcetera. 



fl. C. Russell ; Volcanoes of North America, p. 308. 



