892 



SCmNGK 



[N. S. Vol. IX. No. 235. 



the remainder entered it in the liquid state. 

 It would be a bold petrologist who would 

 insist that it has been demonstrated that 

 the basement complex is simply the molten 

 envelope of the primitive earth solidified in 

 situ, however much he might be disposed to 

 entertain this view among his working 

 hypotheses. It would be petrological 

 hardihood to maintain that it was even a 

 ' sure assumption.' Without denying that 

 the basement complex may be the direct or 

 the indirect offspring of a supposed molten 

 state, no dogma of certitude is now admis- 

 sible on geological grounds. 



The hypothesis of a primitive molten 

 earth is chiefly a deduction from the high 

 internal temperature and from the nebular 

 hypothesis. But it remains to be shown 

 that the high internal temperature may not 

 also be a sequence of an earth which grew 

 up by meteoric accretion with sufficient 

 slowness to remain essentially solid at all 

 stages. An attempt has recently been made 

 to show that a highly-heated state of the 

 interior of the earth would have resulted 

 from the self- compression of the mass dur- 

 ing its accretion, j The methods of reason- 

 ing employed in this attempt were identical 

 with those of Helmholtz relative to the 

 heat of the sun, save that they were ap- 

 plied to a solid body. The computations 

 of Mr. Moulton seem to indicate that 

 gravitative concentration may have been 

 an adequate cause of internal heat. In 

 addition to this tlie thermal effect of mo- 

 lecular change and tidal kneading require 

 recognition. Until these agencies are rigor- 

 ously tested and found wanting, inferences 

 based on the alternative hypothesis can 

 .scarcely be the ground of sure assumption. 

 The irregular distribution of internal heat 

 is more notably in harmony with the hy- 

 pothesis of internal compressive generation 



* A Group of Hypotheses bearing on Climatic 

 Clianges. Jour. Geo!., Vol. V., No. 7, Oct. -Nov., 1897, 

 p. 670. 



than with that which makes it a residuum 

 of a molten state whose temperature should 

 be approximately uniform. If this irregu- 

 larity be assigned to volcanic action it must 

 be remembered that vulcanism is itself a 

 part of the irregitlarity and adds to the 

 burden of explication. Both hypotheses 

 ultimately appeal to the same source, the 

 gravitative descent of the earth's substance. 

 Their differences lie in the modes of action 

 assumed respectively, and these modes are 

 determined by the antecedent conditions of 

 aggregation. Has it been demonstrated 

 that these antecedent conditions were of 

 the one kind and not of the other ? 



Lord Kelvin obviously assumes a nebu- 

 lous state of the earth as the controlling 

 antecedent condition. It is not quite clear 

 whether he adopts the complete gaseous 

 theory of Laplace, including the earth- 

 moon gaseous ring, or not. Apparently, 

 however, he has not adopted the gaseous 

 earth-moon ring, but has substituted there- 

 for a meteoroidal ancestry for the earth, 

 for he says (p. 706): " Considering the al- 

 most certain truth that the earth was built 

 up of meteorites falling together, we may 

 follow in imagination the whole process of 

 shrinking from gaseous nebula to liquid 

 lava and metals, and solidification of liquid 

 from central regions outwards." A little 

 farther ou he speaks of " the gaseous nebula 

 which at one time constituted the matter 

 of our present earth." Without feeling 

 quite certain that I am not in error, I in- 

 terpret these sentences to mean that the 

 matter of the earth was in a meteoroidal 

 condition just previous to its falling to- 

 gether, and that it passed into the gaseous 

 condition as a result of the heat of impact, 

 and that from thence it shrank into the 

 liquid and later into the solid state. If 

 this be correct it would be interesting to 

 learn on what grounds the older hypothesis 

 of a nebulous ring, once regarded as a quite 

 sure assumption, has been abandoned, and 



