424 CARNEGIE INSTITUTION OF WASHINGTON. 



in intensity as depth increases, general disruptions of the molecular 

 attachments are believed to require differential stresses, and these 

 are not generally supposed to reach a high order in the interior. 

 There do not appear to be any cogent reasons why such differential 

 strains as may there arise may not find easement by the idiomo- 

 lecular method, the mass still retaining its rigidity and elasticity, as 

 it does in the zone of observation. 



If there were space to go into details, many successive changes in 

 the energy phases that enter into these idiomolecular actions, as the 

 compression proceeds, would need to be sketched, for the specific 

 paths of energy divide in various directions and proportions. Com- 

 pression in an elastico-rigid body thus differs rather radically from 

 compression in a liquid. 



THE PART PLAYED BY TRUE FLUIDAL ACTION. 



Even though the earth is held to be essentially solid, very important 

 functions are assigned to the relatively small liquefied portions, but 

 only what is essential to the compressive problem can be touched here, 

 and that but briefly. The two postulated sources of liquefaction are 

 the heat derived from compression and that from the disintegration of 

 radioactive substances. The latter, since it can not safely be referred 

 to compression, must be treated as an independent agency. The heat 

 arising from radioactivity may have supplemented the heat arising 

 from compression sufficiently to produce all the liquidity that is cer- 

 tainly known to have arisen. This, however, is uncertain, perhaps 

 improbable. On the other hand, in the present state of evidence, 

 it is doubtful whether compression, of itself, produces liquefaction in 

 the interior. The present trend of growing evidence and of theory 

 favors the view that increased rigidity and elasticity are the normal 

 products of increased pressure in spite of such heat as it develops. 

 Still, when large proportions of highly refractory material are inti- 

 mately mixed with small proportions of easily liquefiable substances, 

 it seems possible that the former may so far bear the brunt of the com- 

 pressive action — taking on additional rigidity — as to permit interstitial 

 bits of the more liquefiable — -and also the more yielding — matter to 

 measurably escape the main stress and become liquefied by the common 

 heat developed by the compression, and so indirectly, though not 

 directly, be liquefied by compression. At any rate, magmas of relatively 

 small volume have come to the surface at close intervals all through 

 the known geologic periods and continue still to come. Their relative 

 smallness is notable and is believed to be significant ; no really great 

 outpours, without intervals between the flows, are known. Some of 

 the batholitic intrusions seem to be more massive, but little is known 

 of the stages of their injection. 



It is important to note that the theoretical curve of temperature 

 assignable to compression rises very slowly in the outer part of the 



