THE EARTH: ITS FIGURE, DIMENSIONS, AND THE 

 CONSTITUTION OF ITS INTERIOR.^ 



By T. C. Chambeblin, Habky Fielding Reid, John F. Hayford, and Fkank 



SCHLESINGER. 



I. 



THE INTERIOR OF THE EARTH FROM THE VIEWPOINT OF GEOLOGY. 



By T. C. Chambeklin. 



For some time past there has been a marked drift of geologic 

 opinion from tlie older tenet of a molten earth toward the conviction 

 that the earth is essentially solid. This trend has been quite as much 

 due to the contributions of kindred sciences as to the growth of 

 geologic evidence, but geology has made its important and concurrent 

 contributions to it. 



The great granitic embossments that constitute the most dis- 

 tinctive feature of the oldest known terranes were formerly regarded 

 as solidified portions of a primitive molten earth and thus seemed to 

 serve as witnesses to the verity of the former liquid state. A few 

 years ago, however, it was determined — almost simultaneously in 

 several countries where critical studies on these formations were in 

 progress — that these granitic masses are intrusive in older formations 

 that had previously been formed at the swface of the earth. These 

 surface formations have thus come to stand as the most ancient ter- 

 ranes now laiown. These earliest accessible deposits imply the pre- 

 existence of a suitable foundation formed at a still earlier date. 

 Neither the surface sediments nor the intrusives give any clear 

 intimation that formations beneath them are different in origin from 

 themselves. So far, then, as the record runs, it testifies to substantial 

 solidity in the outer part of the globe. 



The record implies, indeed, that some molten matter was present, 

 but gives no certain measure of the ratio of the molten to the solid 

 part. At no stage covered by the lithographic record, indeed, is there 



1 Reprinted, by permission, from Proceedings of the American Philosophical Society, 

 September and October-December, 1915. 



225 



