378 CARNEGIE INSTITUTION OF WASHINGTON. 



of their high molecular activity and the limited gravity of the moon. 

 Hence no such supply of gases as is necessaiy to actuate the great explo- 

 sions should have remained. On the other hand, if the planetesimals 

 that entered into the makeup of the moon carried in a certain amount 

 of occluded or combined gases, as they naturally would, and if also the 

 porous mass of the growing body were penetrated by molecular plan- 

 etesimals of the volatile type, as would be almost inevitable under the 

 assigned conditions, and if they were held there by capillary force or 

 surface adhesion until they became entrapped by the continued growth, 

 there would be incorporated in the growing body the potential supply 

 of gas requu'ed for explosive action. There need then only follow 

 central compression, the forcing of the gaseous matter toward the sur- 

 face, and radioactive generation of heat to develop an effective explosive 

 mechanism. The porous structure of the outer part would furnish 

 almost ideal mechanical conditions for effective pit-fornmtion, for the 

 heaping up of symmetrical rims of elastics, for the projection of radial 

 lines of debris, and for the related phenomena that characterize the 

 moon's topography. The surface features of the moon are therefore 

 held to be cogent evidence that the moon escaped a holo-molten state. 

 On the contrary, localized eruptive action might be developed to a 

 remarkable degree from the conditions normally assignable to an 

 accretional formation. 



THE TESTIMONY OF TERRESTRIAL VULCANISM. 



The same line of argument applies to the earth, with the unimportant 

 qualification that our planet holds an atmosphere whose constituents 

 exert a small partial pressure on its surface. To the extent that an 

 atmosphere could be held if the planet were in a molten state, the 

 magma could hold gases in equilibrium with the partial pressures of the 

 enveloping gases. This amount would certainly be limited, and it is 

 to be noted that the partial pressure would be felt by the lavas at all 

 stages of extiiision and would not constitute an explosive agency. 

 To meet the requirements of the case, a competent supply of explosive 

 gases must be concentrated at the point of explosion. A protracted 

 molten state, during which all free and freeable gases should have been 

 boiled out and the excess dissipated, would seem to be a poor prepara- 

 tion for explosive vulcanism. When the critical features of volcanoes 

 are closely considered, they strongly support the view that eruptions 

 are distinctly local and independent. They have no obvious connection 

 with any liquid sheet or reservoir left over from a general molten state. 



THE TESTIMONY OF THE ABERRANT BODIES OF THE SOLAR SYSTEM. 



Interpreted on the planetesimal basis, the normal phenomena of 

 the solar system thus yield various distinctly concordant phases of 

 testimony bearing on the critical points here at issue. To supplement 

 this, it was thought worth while to inquire whether the aberrant phe- 



