696 T. C. CHAMBERLIN 



such a gas content is incompetent to produce explosive eruptions and 

 that such eruptions occur on the earth only when there are special 

 developments or accumulations of gas within or beneath the 

 exploded matter. In a molten earth, stirred during its long cool- 

 ing stages by effective convection,^ the gases set free by the various 

 stages of heat of that period should have been so far brought to 

 the surface and dissipated by molecular activity — except the 

 limited equilibrium amount — that the earth when cooled and 

 solidified should have been as deficient in explosive material as 

 lavas are now found by experiment to be when melted in the open 

 air at the surface and, after a long stage of boiling, cooled to the 

 solid state. In essence, therefore, the case of the earth is the same 

 as that of the moon. The studies of terrestrial volcanoes of 

 recent years have brought forth accumulating evidence that 

 volcanoes are actuated by inborn rather than outside gases, and 

 that they are essentially independent of one another, though of 

 course not independent of common conditions. Their explosive- 

 ness seems thus clearly due to their own individual resources and 

 has no obvious dependence on any molten zone, sheet, pool, or 

 other remnant of a once pervasive liquid state. 



THE TESTIMONY OF THE ABERRANT BODIES OF THE SOLAR SYSTEM 



We have now considered at some length the bearings of various 

 lines of evidence drawn from the normal elements of the solar 

 system. Let us turn for a moment to such suggestions as may be 

 derived from the aberrant members of the system, the meteors, 

 meteorites, and comets. If these are merely aliens that have been 

 introduced incidentally from foreign sources, as some of them may 

 be, there is little reason to expect them to teach much relative to 

 the domestic organization; but if they were born in the system 

 and are products of its dynamics, they may be quite as instructive 

 as the normal members. 



To discuss them with any definiteness, however, it is necessary 

 to postulate the modes by which they came into being. These 

 should reveal why they are aberrant, though products of the same 



' See pp. 481-87 of previous article, this Journal, Vol. XXVIII (1920). 



