204 T. 0. CHAMBERLIN — GROUNDWORK OV EARTh's DIASTROPHISM 



gressively greater per unit mass of increase during the later stages. This 

 bears on the last two subjects discussed, in that it clearly implies pro- 

 gressive compression of the inner parts. This conclusion is supported by 

 cogent theoretical considerations. A similar comparison with the great 

 outer planets is not admissible, for their constitution, their intimate his- 

 tory, and their dynamics are distinctly diflEerent. They appear now to be 

 largely gaseous and to have been gaseous from the outset. Hence they 

 never underwent the sifting of solar material that was necessary to give 

 the stony and metallic substances that make up the main mass of the 

 solid terrestrial planets.^ The giant planets were thus evolved under the 

 sole control of gaseous dynamics, and their material differs radically in 

 proportions from that of the small solid planets. 



An elaborate inquiry was made to see if any part of the great self- 

 compression indicated by the comparison might be explained reasonably 

 by supposing that the larger bodies had a higher content of inherently 

 heavier matter, but the evidence was found to favor precisely the opposite 

 view. Any consistent mode of genesis makes it almost certain that the 

 larger bodies contain relatively more light material than the smaller 

 bodies. It appears, then, that the self -compression of the earth was not 

 only large relative to its neighbors, but that it became increasingly large 

 as the earth-mass grew, and hence that the interior participated in the 

 self-condensing process throughout all stages. 



The Cause of the basal Diastrophism 



The fundamental source of this great self-compression, and of the 

 diastrophism that necessarily accompanied it because of the differentiated 

 and solid state of the earth material, has been definitely implied in the 

 statements already made and needs to be explicitly stated here merely for 

 emphasis. The self-gravity of the assembling mass converted its own 

 potential energy of position into the actuating energy of diastrophism. 

 This potential energy became available for diastrophism simply because 

 it had been conserved in a high degree by the slow orbital process by 

 which the eartli material had been assembled. Secondary causes of dias- 

 trophism, of course, cooperated witli this basal cause at all stages. Dur- 

 ing the formative stages the basal cause of diastrophism was probably 

 more dominant relatively than in the later stages. In these, various 

 minor causes seem to have had a higher proportionate value, but in all 

 stages, I think, they are to be regarded as incidental rather than funda- 

 mental, at least in the main. 



"Diastrophism and tlie formative processes. XII. Tlie pliysical phases of the planetary 

 nuclei during their formative stages. Jour, of Geol., vol. xxviii (1920), pp. 473-504. 



