382 CARNEGIE INSTITUTION OF WASHINGTON. 



4. The inquiry gives no warrant for supposing that any larger pro- 

 portion of inherently heavy matter entered into the composition of the 

 two larger bodies, the earth and Venus, which have the higher densities, 

 than into the two smaller bodies, Mars and the moon, which have the 

 lower densities, but quite the opposite; nor does it justify any other 

 arbitrary supposition to account for the observed densities. The 

 density ratios seem to be a normal effect of the genetic conditions, for 

 they correspond to the ratios of the differential stresses under which 

 the earth and presumably its neighbors were foraied. 



5. The marked increase of density per unit of increase of mass implies 

 that the higher densities of the larger bodies are mass-effects assignable 

 most consistently to compression abetted by the squeezing out of light 

 material and of substances not suited to take on the denser forms 

 required and by readjustments and reorganizations of the material 

 retained in the interest of high density. 



6. As the mean density of the earth is about twice that of its surficial 

 layer, and as a gradation downwards is implied by several lines of evi- 

 dence, the inference follows that the compression and the allied read- 

 justments were chiefly effective in the central parts of the earth — in 

 other words, the central parts were the chief locus of diastrophism, 

 using this term in a comprehensive sense to include all changes of 

 form or density that were recorded in a solid state. The diastrophism 

 in the deeper parts may not improbably have largely taken on the more 

 intimate forms affected by individual molecular changes as observed 

 in metamorphic rocks rather than declared deformations of the crump- 

 ling and contortional order, but these are not necessarily excluded. 



7. Since the implied cause of this chief diastrophism, added mass, 

 came into effect as the growth of the planet proceeded, it follows — 

 when due allowance is made for the possible lag of effect behind cause — 

 that the greatest diastrophism took place while earth-growth was in pro- 

 gress, a conclusion radically at variance with the inherited view that 

 deformations began only after the earth mass was assembled as a 

 Uquid globe and had cooled so far that congelation of its surface afforded 

 the means of a deformative record. 



8. The reexamination of the formative processes assigned by etn 

 planetesimal hj^Dothesis disclosed the inapplicabihty of deductsiqo 

 from unmodified gaseous condensation to the formation of the solid 

 bodies of the solar system from the earth downward. It appeared that 

 their formation must have been rather radically influenced (1) by in- 

 herited motions, (2) by the loss of light material through molecular 

 activity, and (3) by the formation of precipitates and precipitate 

 aggregates. The Hnes of planetary descent for this class of bodies seems 

 to have lain through BrowTiian mixtures and precipitate-aggregates. 

 These, supplemented by planetesimal infall, seem to provide working 

 conditions suited to meet the formative requirements of these solid 

 bodies. 



