692 T. C. CHAM BERLIN 



Reciprocally radioactivity greatly eases the burden laid on 

 compression in the outer part of the earth where it is least compe- 

 tent and where resort was had to igneous intrusions from below to 

 give the crust its observed temperatures. With the addition of 

 the new thermal agency the extrusions are presumed to play much 

 the same part as before but more actively, as they must now be 

 supposed to meet the liquefying effects both of compression and 

 of radioactivity. If there was ground before to question the 

 efficiency of compressional heat, aided by such other sources as 

 were formerly assignable, to give rise to the high degree of igneous 

 activity that marked the Archaean ages and to sustain the lesser 

 igneous action of later periods down to the present, this doubt is 

 amply resolved by the combined efficiency of compression and 

 radioactivity. In any case it is certain that a large amount of 

 energy has been brought to the surface and radiated into space. 



Radioactivity also comes to the aid of other agencies of extru- 

 sion in the peculiar service it renders in opening a path for the 

 outward movement of the liquid matter. In the liquefying pro- 

 cess, as we have seen, the radioactive particles should have been 

 gathered by their self-heating action into the liquid vesicles and 

 have been forced outward with -them. The self-heating property 

 thus became an endowment of the liquid and gave to it thermal 

 efficiency in dissolving and fluxing its way. This efficiency was 

 continually renewed by the progressive disintegration of the radio- 

 active atoms. It is not improbable that the liquid threads were 

 thus aided in a very special way in boring upward, for it seems 

 obvious that the part of the liquid which carried most of the self- 

 heating constituent would come to have the highest temperature, 

 the lowest specific gravity, and the largest gaseous factor — for 

 the disintegration produced gas emanation and helium in addition 

 to the gases generated by the heat alone — and hence would take 

 the uppermost position and bring its liquefying influences to bear 

 on the solid matter which lay between it and the surface toward 

 which it was pressed. The very mechanism may thus have kept 

 the most effective part at the point most critical to its ascent. 



While this outline falls far short of an adequate discussion of 

 the relations of radioactivity to the planetesimal hypothesis, it 



