248 H. L. FAIRCHILD — GEOLOGY UNDER PLANETESIMAL HYPOTHESIS 



face of the globe. It would seem as if there must have been a long stage 

 of conflict between the interior heat and the superficial cold. In the 

 early stages of the growing globe the water was forced toward the surface 

 only to be buried under the infalling material of world-growth. Subse- 

 quently the pressure and rising temperature forced it further surface- 

 ward. This idea implies that much of the deeper interior may be com- 

 paratively dehydrated, which may help to explain the anhydrous state 

 of vast outflows of molten rock. 



It is probable that the moon now represents the pre-atmospheric 

 stage of world-growth. Under the old hypothesis, the moon is sup- 

 posed to have absorbed its fluid envelopes by interior cooling and 

 resulting porosity, and the earth to be destined for the same fate, on 

 the assumption that the amount of water on the earth is diminishing 

 and the amount in the earth is increasing. The new hypothesis holds 

 just the opposite view. The moon, under the new view, is not an illus- 

 tration of a globe in old age or of completed evolution, but is an exam- 

 ple of arrested development. The moon's growth was stopped by lack 

 of building material before its gravitational power was competent to 

 hold an atmosphere. Its internal heat was apparently sufficient and its 

 volcanic action pronounced, but its gaseous exudations seem to have 

 been lost into space or frozen at the surface. If the planetesimal hypoth- 

 esis be true in its postulate of world origin and growth, then in the 

 moon we may have a visible illustration of an early stage in the process. 



The mineral contents of sea water are held by the old hypothesis to 

 be derived from decay of primitive rocks, except to whatever extent 

 they were indigenous to the nebulous envelopes. The new hypothesis 

 allows derivation in part from superficial rock alteration, specially the 

 carbonates, but suggests emphatically that most of the saline mineral 

 content of the ocean has been derived, like the ocean itself, from subter- 

 ranean sources. 



Earliest sedimentary Rooks 



Under the conception of a globe cooling from a superheated state, the 

 CDiiclusion seems inevitable that the first deposits should have been 

 chemical precipitates from the ocean of hot water. This idea has been 

 the subject of speculative writing, but no rocks have been found which 

 appear to have had such genesis, although, if such precipitates were 

 ever formed, they should be discovered somewhere in recognizable form. 

 The conception has been barren of results in petrography. 



The nebular hypothesis requires that the globe should have been fully 

 formed before the surface or epigene agencies began their work, and that 

 all the vast deposits of fragmental origin, the clastic rocks, have been 



