356 CARNEGIE INSTITUTION OF WASHINGTON. 



GEOLOGY. 



Chamberlin, T. C, University of Chicago, Chicago, lUinois. Study of funda- 

 mental problems of geology. (For previous reports see Year Books Nos. 

 2-12.) 



The studies of the year have followed the lines set forth in previous 

 reports, especially that of the last year, and in addition progress has 

 been made in putting into the form of definite w^orking tenets for geo- 

 logical use the results reached in the course of these studies. Recent 

 advances in related investigations, especially in tidal, seismic, geodetic, 

 volcanic, and associated lines, have made such radical contributions to 

 earth science as to require important revisions of geologic doctrine. An 

 effort has therefore been made to combine these with the results spring- 

 ing from the planetesimal hypothesis into working concepts for use and 

 for test in concrete application. Since the first outline of the planetesi- 

 mal view of the origin of the earth was set forth in the Year Book (No. 3, 

 pp. 217-219) the new theory of genesis has been called upon to face 

 unexpected criteria arising from the following discoveries and deter- 

 minations whose bearings are radical : 



1. It has been discovered that Jupiter and Saturn have each a satel- 

 lite revolving in a retrograde direction in addition to several revolving 

 in a forward direction. These significant discoveries are not only in 

 accord with the planetesimal hypothesis, but are in special concurrence 

 with it in that the orbits of the satellites of retrograde revolutions are 

 more eccentric and otherwise aberrant than those of forward revolu- 

 tions as anticipated by Moulton's deductions from dynamic considera- 

 tions. 



2. Geodetic determinations by Hayford and others imply that the 

 materials of the earth beneath the great basins are higher in specific 

 gravity than the matter beneath the great elevations and that this 

 difference in specific gravity descends to very considerable depths — at 

 least 70 miles and probably nuch more. "WTiile it is difficult to see how 

 this deep differentiation of specific gravity could have arisen out of a 

 once fluid globe, it is a probable result of a slow accretion differentiated 

 by diastrophic, hydrospheric, and atmospheric action. 



3. The discovery of radioactivity has led to studies on the distribu- 

 tion of radioactive substances and to computations as to the heat 

 generated by them, from which it appears probable that radioactive 

 substances are confined mainly to the outer part of the earth. Such a 

 concentration is quite in harmony with the hypothesis of volcanic 

 action that has been deduced from the planetesimal h^'pothesis which 

 limits internal liquefaction to very local portions of the interior mass 

 which are eutectic in nature and which become specially heated by 

 their content of radioactive matter and are forced by tidal and other 

 internal stresses to work their way to the outer zone essentially as fast 



