FUNDAMENTAL PROBLEMS OF GEOLOGY. I99 



I 



system is attained, and then, but not till then, enter upon an evolu- 

 tion into a sun-and-planet system ? If the swarm was organized on 

 the collisional basis, nothing but a negative answer seems to me 

 possible. If the meteorites could be supposed to so come together 

 as to revolve in harmonious orbits about a common center, on the 

 planetary basis, the assemblage might perhaps be perpetuated ; but 

 this takes the case out of the typical meteoritic class, as here defined, 

 and carries it over to the planetesimal. 



Under the conditions of the case as thus brought out, I have been 

 unable to discover a probable method by which a meteoric nebula of 

 the quasi-gaseous or collisional type can grow up de novo by the 

 assemblage of dispersed meteorites or by the aggregation of chaotic 

 matter if the material were endowed with the present momentum of 

 the average matter of the stellar s3-stem. 



(2) The study of the possibilities of the origin of a meteoritic nebula 

 of the collisional or quasi-gaseous type from the dispersion of some 

 previous large body recognized three possible phases : (^) dispersion 

 by explosion ; ij)) dispersion by collision ; and {c) dispersion by tidal 

 disruption. 



It is difficult to find any tangible ground for postulating an ex- 

 plosion competent to disperse to the requisite degree a body of the 

 mass of the solar system ; but if this difficulty be passed and the 

 requisite force be assumed, it must apparently act radially, in the 

 main, and after the matter has made its outward excursion and is 

 arrested by gravitation, it must return on nearly direct lines and 

 collide at the virtual point of departure. If the outward movement 

 were of nebular extent the collision attending the return must have 

 developed sufficient heat for the conversion of the whole into a gas- 

 eous body, and the sub.sequent evolution must have followed gaseous 

 lines. It is not apparent how anything properly analogous to a 

 meteoritic swarm could be developed by this process. If the hypo- 

 thetical explosion could be supposed to be sufficiently violent to 

 project the constituent matter beyond the control of the system, the 

 di.spersed parts might become truly meteoritic, but their courses 

 would be indefinitely divergent, and there would be no assignable 

 agency for their reassemblage. The constituents would pursue 

 individual courses and be subject to sporadic capture essentially as 

 in the case previously considered. 



Regarding the possibilities of dispersion by collision, it seemed 

 necessary to suppose that the heat developed would be so great as 

 to convert the main mass into a gaseous state. If the collision were 



