226 THE AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. 



B}^ w.\Y of preface it may be remarked that the postulate of a white- 

 hot liquid earth does not rest on any conclusive geological evidence, 

 however generally it may be entertained as a probable hypothesis. 

 Students of the oldest known rocks are not yet agreed that these are 

 all igneous even. But granting that they may be all either igneous or 

 pyroclastic, there is a wide logical gap between this admission and the 

 postulate that they were all liquid at one time and enveloped the whole 

 earth. Looking quite in the opposite direction is the testimony of the 

 complex structure and intricate combination of rocks, diverse at once 

 in chemical, mineralogical, and structural characters, which the base- 

 ment complex presents. The relations of the great batholite-like 

 masses to the enveloping foliated rocks, and of analogous combinations 

 of intrusive aspect, imply the presence of a portion of the basement 

 complex in the already solid state when 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 simpl}^ 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 admissible 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 accre- 

 tion 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 -compres- 

 sion of the mass during its accretion.^ The methods of reasoning 

 employed in this attempt were identical with those of Helmholtz rela- 

 tive to- the heat of the sun, save that they were applied 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 the thermal effect of molecular change and tidal knead- 

 ing require recognition. Until these agencies are rigorously 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 hypothesis of 

 internal compressive generation than with that which makes it a resid- 

 uuin of a molten state whose temperature should be approximately 

 uniform. If this irregularity be assigned to volcanic action, it must 

 be remembered that vulcanism is itself a part of the irregularity and 



^ " A group of hypotheses bearing on climatic changes."— Jour. Geol., Vol. V, No. 

 7, •October-November, 1897, p. 670, 



