260 H. L. FAIRCHILD — GEOLOGY UNDER PLANETESIMAL HYPOTHESIS 



should be found for the misleading terms " crust," " nucleus," and 

 " igneous." 



Irregularities of the Earth's Figure 



Although much has been written on the subject of continental forms, 

 and even geometric and crystallographic principles have been applied, 

 yet it must be admitted that no clear meaning has been found for the 

 relief forms of our globe. Perhaps if the efforts had not been made 

 under a false conception of earth genesis better results might have been 

 attained. It seems likely that the relief forms are fortuitous, due to 

 irregular accretion and unequal density, and that they have no genetic 

 or structural relationship. This conclusion is strengthened when we 

 consider that the configuration of the exposed lands is greatly changed 

 by relatively small differences of vertical position, and even more im- 

 portant, by the almost certain fact that the disposition and relation of 

 lands and sea have been in former ages radically unlike the present. 

 This latter fact does not entirely contradict the principle of relative per- 

 manence of the continental and oceanic areas, but suggests that the 

 principle must not be applied too rigidly. 



Investigations seem to prove the unequal density of the earth, and the 

 same conclusion is reached by physical deduction. The fact of epeiro- 

 genic oscillations and orogenic uplifts would seem to imply that under 

 slowly applied and long continued forces the deeper rocks of the globe 

 are viscous. This seems to require isostatic equilibrium, which in turn 

 implies that the sub-oceanic portions of the lithosphere must be denser 

 than the continental areas, and that the lithosphere of the southern or 

 oceanic hemisphere must be denser than that of the northern or conti- 

 nental hemisphere. These conclusions as to the varying density of the 

 earth may not be wholly contradictory to the nebular hypothesis, but 

 they are certainly more favorable to the new hypothesis. Long dura- 

 tion of gaseous and liquid stages in the life of the globe would favor dif- 

 fusion, convection, and resulting homogeneity. The new hypothesis, 

 forming the globe from cold solid materials, favors heterogeneity, and is 

 in better harmony with the geologic facts and the philosophic deduc- 

 tions relating to the earth's structure. 



Life on the Earth 



Under the new hypothesis the problem of the origin and duration of 

 life may be quite a different matter from the same problem under the 

 old hypothesis. With the high temperatures required by the nebular 

 hypothesis, life was at first impossible, and the low temperature of space 



