REPORT OF THE DIRECTOR I92O-2I 141 



of the deformative agencies in the early history of the earth, and 

 stated in " The Origin of the Earth," that periodical changes in 

 the rate of rotation have been of the greatest importance among 

 the shaping agencies of the framework of the earth. 



The master features of the latter are seen by Chamberlin according 

 to the ingenious hypothesis developed by him (op. cit.) "in a 

 segmentation that sprang from primitive shrinkage stimulated 

 and shaped by oscillating rotation and tidal strains." This seg- 

 mentation would take place at times when the polar areas were in 

 tension through a cracking that would produce yield zones at 120 

 to each other, that pass from the poles to the fulcrum zones not 

 far from 30 Lat. N. and S., while between them there should be 

 oblique trends. The protrusive effects of the rotational stresses 

 are supposed to have been mainly felt at the angles where the 

 yield tracts joined one another, and subordinately along the yield 

 tracts themselves. The continents are therefore held to have 

 grown up from these angles as centers while the oceans formed 

 in the depressions between. 



We can not enter here more fully into this fascinating hypothesis 

 which is fully set forth and illustrated in " The Origin of the Earth," 1 

 except to state that Chamberlin obtains three oval oceanic »basins 

 on the northern hemisphere, namely, the Pacific, North Atlantic 

 and the Caspo-Mediterranean cluster of depressions, and three 

 on the southern, namely, the south Pacific, south Atlantic and 

 Indian oceans. The continental clusters are North America, South 

 America, Eurafrica, Asia, Australia and Antarctica. 



It will be seen at once that this arrangement of the primordial 

 continents and oceans differs from the one at which we have arrived 

 from the consideration of the Precambrian trend lines. It is, 

 however, also obvious that Chamberlin' s arrangement of the 

 primeval continents and oceans is equally different from that found 

 by paleogeographers at the beginning of the Paleozoic era; and 

 further that it is based on the conception of a gradual growth of the 

 earth from planetesimals without reaching a molten state, a view 

 against which Barrell and Daly, as noted before, have advanced 

 arguments tending to show that a molten condition of the surface 

 of the fully grown earth must be postulated to explain various 

 facts, and they have for that reason considered Chamberlin's seg- 

 mentation hypothesis as not well supported. 



However that may be, it is sufficient here for our purpose to 

 emphasize the fact that Chamberlin's hypothesis is designed to 



1 See also article in Scientific Monthly, iqi6, v. 2, on the " Evolution of the 



Earth." 



