54 PROCEEDINGS OF THE AMERICAN ACADEMY. 



general conception has been independently stated by H. J. Johnston- 

 Lavis, one of the world's most experienced students of volcanoes. Only 

 quite recently has the writer found that he had been anticipated by 

 Johnston-Lavis in the root idea, as expressed in brief notes published 

 in the Geological Magazine.® It is a source of genuine satisfaction to 

 find a fellow adventurer in an almost pathless field of investigation, 

 and, yet more, to find in that companion a distinguished specialist. 



The Substratum. 



Similarly, the writer has found that he has been anticipated in the 

 view that the heat-bringer in all Paleozoic and later igneous action is 

 a general basaltic substratum underlying the shell of tension. 1° The 

 essential point was stated by Cotta on page 78 of his " Geologische 

 Fragen," published in Freiberg in 1858, and by W. Lowthian Green on 

 page 61 of his "Vestiges of the Molten Globe," Part II, published in 



^ 17, 246 and 344 (1890). A fuller statement by the same author appears 

 in the Geological Magazine, 36, 433 (1909). 



" Cf. R. A. Daly, Amer. Jour. Science, 15, 294 (1903). 



The writer is clearly conscious that this assumption of an uncrystallized 

 general substratum conflicts with the planetesimal hypothesis of the ecarth's 

 origin, as stated by Chamberlin. Wliatever be the mode of assemblage for the 

 earth's materials originally, it is extremely difficult to accept the view that, when 

 the planet approached its present size, it could have avoided a stage where it 

 was molten all over the surface. Lunn's temperature-depth curve (Chamberlin 

 and Salisbury's "Geology," 2d ed., 1, 564, 1906) for the earth, computed 

 on the accretion hypothesis, shows temperatures of from 10,000° to 20,000° C. 

 in the interior. Since, on the hypothesis, the mode of accretion afforded a 

 very heterogeneous mass at the beginning, there must have been a gravitative 

 readjustment of the materials rendered fluid by the high temperature of the 

 interior. The less dense matter, rising from great depth, would bring to the 

 surface a large proportion of its enormous heat-content, ultimately fusing a 

 surface shell of great depth. In other words, the earth-furnace imagined by 

 Chamberlin and Lunn would melt its own walls. 



Another serious objection to the hypothesis that the earth has been largely 

 solid (crystalline) throughout its history is the fact that each of the planets, 

 Jui)iter, Saturn, Uranus, and Neptune, has a density appropriate to a gaseous 

 condition and to very liigh temperature even in the surface shell. Again, if the 

 moon were never fluid at the surface, its matter has been fluid very close to 

 that surface; every square meter of its visible surface seems to have wit- 

 nessed igneous action. So far, the published statement of the planetesimal 

 hypothesis has not discussed the earth's history in terms of the facts known 

 about its fellow members in the solar system. Since both the gas-nobula and 

 planetesimal-nebula hypotheses seem to demand an incandescent, molten 

 stage for the earth, the present writer is inclined to doubt that the geologist, 

 for most of his thinking, needs a decision as to the truth of either hypothesis. 

 That is a matter for cosmogony and astrophysics. 



