DIASTROPHISM AND THE FORMATIVE PROCESSES 143 



by their own gravitative power. Incidentally molecules might be 

 entrapped or occluded within these small bodies, or chemically 

 united with them, or possibly even held against them by surface 

 adhesion; but, otherwise, free molecules would rebound and escape 

 control. Those soHd particles that were highly elastic would also 

 largely escape by rebound ; those that were inelastic would more "* 

 largely remain adherent after impact. Malleable substances like 

 the metals would be Hkely to weld and cohere by collision. In 

 general, these cohering bodies belong to the heavier order of sub- 

 stances, and so bodies formed in this way would be for the greater 

 part selectively heavy. 



If we could be sure that the chondrules of meteorites represent 

 accretion of the foregoing type — a hypothesis to be seriously con- 

 sidered — it would give a specific insight into the cosmic aggregates 

 of this order, for then they might be said to be dominantly formed 

 of ferro-magnesian siHcates, nickel-iron, and metalKc sulphides, but 

 it would be premature to draw this conclusion. 



At any rate, since, on the one hand, these small bodies could 

 not hold free molecules of the lighter order, and, on the other hand, 

 the conditions were favorable for the aggregation of metallic sub- 

 stances, heavy silicates, sulphides, and so forth, it seems safe to 

 conclude that these small aggregates contained a relatively high 

 proportion of inherently heavy matter. 



It seems to follow then that, if Mars, Venus, the earth, and the 

 moon could have been gradually built up by the assemblage of 

 particles, crystals, pellets, nodules, or even more considerable 

 masses formed in this selective way, the percentage of heavier con- 

 stituents could scarcely have been less in the earher stages and in 

 the smaller bodies than in the later stages and in the larger bodies, 

 while they were probably somewhat distinctly greater; for in so 

 far as these bodies succeeded in becoming large, they could then, but 

 only then, have held the Hghter order of molecules in a free state 

 and thus have reduced their mean density. When atmospheres 

 and hydrospheres were thus added, the processes of oxidation, 

 hydration, and carbonation became important and the groundwork 

 was laid for petrological derivatives from the products of these 

 processes. A large class of the rocks and minerals of the outer 



