THE ORIGIN OF THE EARTH. 9 



reached the surface, and that there was then a zone of liquid between 

 a solid crust and a solid center. This zone is thought by some to have 

 remained to the present time; by others to have solidified later, and 

 by still others to have partially solidified so that the crust is joined 

 to the central mass by solid supports, while residues of liquid have 

 been left between in certain portions. By postulating these liquid 

 residues, a source for the lavas ejected at later stages is hypothetically 

 provided. 



Hypothetical gaseous center. — Against the view of a solid center 

 it is urged that the temperature of the gaseous globe at its center must 

 have been above the critical point, and must have risen with progressive 

 condensation so long as it remained in the gaseous state, and hence 

 that the gaseous center could not have taken on the solid state. A. 

 globe with a gaseous center is therefore a fourth conception. How 

 this is to be reconciled with the evidences of rigidity and other physical 

 phenomena of the globe is not obvious. 



There thus arise from the Laplacian hypothesis four general con- 

 ceptions of the state of the body of the earth: (1) that it is all liquid 

 within and merely crusted over, (2) that it is solid at the center and 

 crusted over on the surface, with a liquid or partially liquid zone between, 

 (3) that it is solid throughout, and (4) that its center is gaseous and 

 its exterior solid. 



Part played in geologic doctrines. — The view that the earth was 

 once in a molten state very naturally led to certain inferences as to 

 the internal arrangement of the matter, the original form of the sur- 

 face, the state of the primitive atmosphere, and to a long chain of 

 dependent interpretations; and so the hypothesis has become inter- 

 woven with the interpretations of nearly all the great phenomena of 

 geology. The changes in the form of the earth, the warping of its 

 crust into ocean basins and land protrusions, its wrinkling into moun- 

 tains, its fissurings and faultings, its risings and fallings, its volcanoes 

 and its earthquakes, have been usually regarded as the natural sequences 

 of a cooling globe. So, too, the consumption of the atmosphere in 

 the formation of the oxides, carbonates, and carbonaceous deposits, 

 and the absorption of the ocean into the body of the earth, are cur- 

 rent doctrines founded on the Laplacian hypothesis. 



Supporting phenomena. — In favor of the Laplacian hypothesis 

 stand the unquestioned facts that the interior of the earth is hot, that 



