VULCANOLOGY AND SEISMOLOGY. 477 



Ou the other hand, paroxysmal eruptions often be^in with a violent 

 burst, followed by a series of ex])l()sions, with but little extrusion of lava, 

 and sometimes with absolutely none at all, only scorii© being emitted, 

 as at Cosagnina and Krakatoa. The author would account for the pres- 

 ence of great quantities of water m some eruptions by the admission of 

 the surface waters, or sometimes of sea water, to the volcanic duct dur- 

 ing the erui)tion itself, and gives diagrams of the altered water levels 

 about a volcano during an eruption to show the possibility of such ad- 

 missions. Concluding, then, that water plays only a secondary part in 

 originating volcanic iJheuomeun, he is inclined to recur to the old liy- 

 pothesis of a comparatively thin, flexible earth-crust resting upon a 

 molten substratum; but instead of adopting anew the theory of a fluid 

 interior to the earth, which jihysical reasoning has shown to be untenable, 

 he thinks the phenomena are best accounted for by the supposition of a 

 thin crust, resting oii a viscid layer also of no great thickness, and wrap- 

 ping round a solid nucleus. He concludes that the viscid magma thus 

 compressed between two solid layers by the secular contraction of the 

 globe is extiuded where it may find or make an opening. And while 

 the extravasation of lava is due to these causes, the presence of vapor 

 is due only to the surface and underground waters with which the lava 

 comes in contact as it rises through the volcanic duct. {Mature, xxxi : 

 592.) 



Similar opinions as to the part played by water in volcanic outbursts, 

 and the source from which the water is derived, were expressed before 

 the Geological Society by H. J. Johnston-La vis. {Nature, xxxii: G9.) 



The discussion of the theoretical form of volcanic cones, begun by Pro- 

 lessor Milne in 1878 and 1879 {Geol. Mag.), is renewed and carried on by 

 George F. Becker. {Am. Jour. Sci., xxx : 283.) Milne had regarded the 

 problem as being that of the l<»rm assumed by loose materials, cinders, 

 ashes, etc., and concludes that it would be that generated by the revolu- 

 tion of a logarithmic curve round its asymptote. But Becker regards the 

 mountain as essentially a continuous mass, and deduces the equation of 

 the curve, which by its revolution will generate the finite unloaded (column 



X X 



Of " least variable resistance," for which he finds ^ = ^ " ^ * " . This 



c 2 



is a special case of theequation j^ _ ^\ f- ' ^_ b f ^ which he has elsewhere 

 shown to characterize the arrangement of sheets of rock in a complex 

 fault, and which belongs also to several other physical phenomena. On 

 comparing graphically this theoretical curve with actual outlines drawn 

 from photographs of volcanic; cones, as with Fusiyama and Kumagatake 

 in Japan, and Hood and Popocatapetl in America, the similarity of the 

 several outlines is at once evident. 



Yelain's book "Les Volcans" is briefly reviewed by Captain Button, 

 stating the contents of the several chapters, with comments thereon. 

 (Science, vi : 255.) 



