February 19, 1886.J 



SCIENCE. 



159 



voirs of liquid rock and be absorbed by it, as any 

 gas would be by a liquid, is regarded as entirely 

 possible, and not improbable. But great emphasis 

 is properly laid upon the fact that this gradual 

 absorption of hot vapor by hot lava would not 

 create any tendency in the lava to explode or 

 erupt, unless accompanied by a diminution of 

 pressure or increase of temperature ; and it is 

 demonstrated at considerable length that no 

 changes of temperature or pressure in the magma, 

 of sufficient magnitude to merit consideration, are 

 possible : consequently the balance of probability 

 is regarded as inclining decidedly against the 

 hypothesis that water is the cause of volcanic ac- 

 tion. It does not appear, however, that Captain 

 Dutton has taken any account of the important 

 consideration, that, by the rising of the isogeo- 

 therms, water-impregnated portions of the earth's 

 crust may conceivably attain a high degree of 

 liquidity and expansive force ; i. e., be made 

 eruptible. 



The hypothesis that volcanic energy is due to 

 the penetration of oxygen to the unoxidized earth- 

 matter below the crust is also rejected, mainly 

 because it appears to be insusceptible of proof or 

 disproof, postulating conditions beyond the reach 

 of argument, but partly on account of the diffi- 

 culty of finding a sufficient amount of oxygen. 

 The statement, however, that some naturalists 

 imagine that the earth's interior is imperfectly 

 oxidized is certainly unwarranted, in view of the 

 fact that basic lavas contain metallic iron and a 

 vast amount of iron in a low state of oxidation. 



Mallet's theory, that volcanic heat results from 

 the mechanical crushing of the rocks when the 

 crust yields to the powerful horizontal pressure 

 due to the cooling of the interior, and mountain- 

 ranges, rock-folds, and faults are produced, shares 

 the same fate ; chiefly because it is now probable 

 that the cooling of the earth has been up to this 

 time comparatively superficial, the infra-crustal 

 regions being still as hot as ever. But Captain 

 Dutton's argument is not conclusive, since he has 

 simply shown that the corrugation of the crust 

 must be ascribed to some other cause, such as the 

 diminution of the earth's oblateness in consequence 

 of the retardation of its rotation by tidal friction. 

 The corrugation itself is an unquestioned fact, 

 and, however produced, must have been attended 

 by an enormous development of heat. 



The fourth hypothesis examined assumes a local 

 development of heat in the earth by unknown 

 causes. This cuts the Gordian knot instead of 

 untying it, but is rejected because its conditions 

 preclude all discussions of its validity or adequacy. 

 Relief of pressure would greatly promote the 

 liquefaction and elastic expansion of lavas ; but 



this is unconditionally rejected as a cause of erup- 

 tions, since denudation, the only cause of di- 

 minished pressure which Captain Dutton recog- 

 nizes, cannot be correlated in its distribution with 

 active volcanoes. 



Having thus discredited all hypotheses of the 

 origin of volcanic heat heretofore proposed, Cap- 

 tain Dutton advances no new view, but coolly de- 

 molishes our hope with the statement that Mauna 

 Loa and Kilauea do not throw any more light 

 upon the general problem than other volcanoes. 

 He proceeds to show, however, that in other direc- 

 tions they have contributed something to our 

 knowledge of volcanism. They are at once the 

 largest and most active of volcanoes, activity 

 being measured by the outflow of lava, and dissi- 

 pation of energy. They agree with active volcanoes 

 in general in standing on an area of elevation. 

 That Hawaii has risen nearly three thousand feet 

 in comparatively recent times, is regarded as 

 clearly proved by the elevated beaches and ter- 

 races. The problem of the causes of elevatory 

 movements is then attacked, and the numerous 

 hypotheses are reduced to two alternative proposi- 

 tions ; viz., the elevated portion of the earth has 

 experienced an increase of matter, or it has 

 undergone expansion. While local increments of 

 mass are not ignored, the expansion hypothesis is 

 accepted as the one agreeing best with the ob- 

 served facts ; and the tangential thrusts of the 

 earth's crust are definitively rejected as a primary 

 cause of vertical movements. Our author wisely 

 refrains, however, from estimating what propor- 

 tion of the altitude of the Alps and other mountain- 

 ranges is due to the crumpling of their strata ; this 

 crumpling being unquestionably due to horizontal 

 thrusts, and amounting in the Alps, according to 

 Heim, to seventy-four horizontal miles. Hawaii, 

 we are told, floats high because of the lightness 

 of this part of the earth's crust, its relatively low 

 density being due in part to its high temperature, 

 and in part to the porosity of the lava, and the 

 numerous and often large tunnels by which the 

 entire island appears to be honeycombed. But no 

 calculation is given of the increase of temperature 

 required in a thin crust, with a reasonable co- 

 efficient of expansion, to produce an elevation of 

 two or three miles in a non-volcanic region. It is 

 not easy to see how the expansion hypothesis can 

 survive application to really important instances 

 of elevation. 



Captain Dutton regards the Hawaiian volcanoes 

 as immense columns of liquid lava with their ac- 

 cumulated overflows ; and the upper ends of these 

 columns, whether frozen over or exposing fiery 

 lakes to the sky, are believed to be fundamentally 

 unlike the craters of ordinary volcanoes. The 



