48 PROCEEDINGS OF THE AMERICAN AC.U)EMY. 



Page 



Vulcanism originating in Satellitic Injections 108 



Kilauea the Vent of a Satellitic Injection 109 



An Icelandic Example 116 



Tertiary and Older Vents from Satellitic Injections ; Suabian 



and Scottish Examples 117 



A Necessary Division of Central Vents 118 



General Summary 119 



The Problem. 



Volcanic action is the working of the extrusive mechanism which 

 brings to the earth's surface rock-matter or free gas, initially at the 

 temperature of incandescence. The mechanism involves the localiza- 

 tion, opening, and shaping of the vent ; the persistence of a vent as 

 an open channel during seconds, days, years, centuries, or milleniums ; 

 the conditions for lava outflow, for gas and vapor outflow, and for the 

 separation of gas or vapor from lava ; the conditions leading to the 

 periodicity of eruption at central vents ; and those leading to chemical 

 variations in the erupted magma. 



Since the days of the Greek philosophers thousands of memoirs have 

 touched upon this complex problem of terrestrial dynamics, but geolo- 

 gists are still looking for a generally acceptable solution. Within the 

 last ten or twelve years the variety of new suggestions affecting the 

 very core of volcanic theory has been, perhaps, as great as that of any 

 previous decade. In the varying chemical affinities of water and silica 

 for the bases of rock-matter at different temperatures, Arrhenius finds an 

 essential condition of all vulcanism. He therefore attempts to support 

 the time-honored hypothesis that the vapor of meteoric or marine water 

 absorbed in plutonic magma is the prime motor in eruptions. ^ On the 

 other hand, Brun holds that water is quite unessential to eruption of 

 the first order, and he believes he can prove his thesis by actual 

 analysis of the volcanic emanations.^ Again, Chamberlin explains 

 vulcanism as due to the extrusion of magmatic tongues, which, by tidal 

 stresses, are slowly kneaded out of the deep interior of the otherwise 

 solid earth.3 In entire contrast to that hypothesis, Dutton has come 

 to the belief that the indications are that most of the volcanic erup- 

 tions originate at depths between one mile and two and a half miles.* 



1 S. Arrhenius, Geol. Foren. i Stockholm Forhandl., 22, 395-419 (1900). 



* A. Bnm, Archives des sciences physiques et naturelles, Geneva, fevrier, 

 1909; f6vrier, 1908; novembre, 1906. Le Globe, octobre, 1907. 



3 T. C. Chamberlin and R. D. Salisbury, Geology, 1, 632 (1906), and 2, 

 104 (1906). 



* C. E. Dutton, Volcanos and Radioactivity, 1906, p. 5 (Paper read before 

 the National Academy of Sciences, April 17, 1906), published at Englewood, 

 N.J. 



