176 Mevieus — Professor T. C. Chafnberlin's Radio-activity. 



T 



III. — Radio-activity and Geology. 



^s of radio-activity on geology are discussed by 

 Professor T. C. Chamberlin {Journ. Geol., xix, November- 

 December, 1911). He refers first to the old view that " the primitive 

 gaseous or quasi-gaseous earth-mass was held to have passed later 

 into a molten globe, and the subsequent incrusting of this to have 

 entrapped in the interior the heat supply of subsequent ages". 

 To the condensation of the nebula, whether gaseous or a quasi- 

 gaseous meteoric swarm, was attributed the intense heat. An 

 alternative view, developed by the author before the discovery of 

 radio-activity, was the planetesimal hypothesis, which was " built 

 on the belief that earth grew up gradually by the slow accession of 

 discrete orbital matter", and that "the internal heat arose mainly 

 from the self-compression of the earth-mass as it grew ". The chief 

 purpose of the present paper is to set forth the " harmony between 

 the new light shed by radio-activity and the tenets of the planetesimal 

 view". The original source of radio-active substances, so far as 

 known, is in the igneous rocks ; except in meteorites which appear 

 to contain but meagre amounts of the substances, accessions of radio- 

 active material from without the earth has not been demonstrated. 

 It is pointed out tliat " from the igneous rocks the radio-active 

 substances are dissolved and disseminated through the waters and 

 carried wherever they go, while from both the rocks and the waters 

 the emanations are given forth into the atmosphere". Therefore it is 

 that radio-active matter is found "in practically all the rocks of the 

 surface of the earth, in practically all the waters, and in praclically 

 all the atmosphere ". 



The author deals with the inference that liquefaction and eruption 

 of the igneous rocks are dependent on the heat derived from radio- 

 activity. "Weathered igneous rocks are found to carry less radio-active 

 matter than fresh rocks; nevertheless, soils "still retain notable 

 radio-activity, but a part of this is probably a redeposit from the 

 atmosphere". 



The distribution of volcanoes past and present is referred to. The 

 primitive shields, scarred with intrusions, are almost immune now ; 

 but they have suffered denudation, and "according to the hypothesis 

 of concentration at the surface, this lost matter carried a relatively 

 high proportion of radio-active substance ". 



The author supports the view, held by some geologists, that while 

 "the rise of the denuded embossments of the crust was attended 

 by elastic expansion of the whole sector of the earth beneath . . . 

 that the protruding portions of the continents tend to lateral creep, 

 and that this carries with it tensional effects as well as some further 

 elastic expansion. At the same time the penetration of surface-water 

 is promoted, and this aids effectively in carrying off the heat of the 

 outer crust ". 



It is interesting, therefore, to remember that "the movement of 

 igneous matter and of waters and gases heated by it has been made to 

 play an essential part in the working concepts that have been based 

 on the planetesimal hypothesis ". 



