366 CARNEGIE INSTITUTION OF WASHINGTON. 



in these plants. Experiments have been carried on to determine the 

 fluctuation in the percentage of rubber at different seasons and under 

 varying ecologic conditions. Comparisons have been made between 

 the original stands and second-gi'owth shoots, as well as the study of the 

 behavior of plants after cropping. Seeding experiments have not yet 

 been conducted on a large scale, but both germination and garden 

 tests indicate that there will be no difficulty in growing the plants from 

 seed. 



GEOLOGY. 



Chamberlin, T. C, University of Chicago, Chicago, Illinois. Study of Fun- 

 damental Problems of Geology. (For previous reports see Year Books 

 Nos. 2-18.) 



The principal work of the year has been a comparative study of the 

 earth, Venus, Mars, and the moon, -svith special reference to the 

 relative amounts of shrinkage they underwent during their formative 

 stages and the light this might throw on the deformations recorded in 

 the earth's great features.^ Incidentally the inquiry led to a special 

 consideration of the formative processes themselves. This appeared 

 essential because estimates of deformation under the molten and the 

 accretional hypotheses, respectively, are rather radically different 

 not only in amount and kind, but also in the time of occurrence. 

 Under the molten hypothesis, no deformation, in the ordinary geological 

 sense of the term, has been assigned or seems assignable until the fluid 

 state was at least partially replaced by a solid crust, and this crust only 

 began to form after the assembling process was essentially complete. 

 During the assembling the fluid state offered ideal opportunities for 

 chemical combination and physical adjustment, so that, except in so far 

 as heat prevented, the potential resources of shrinkage should have been 

 essentially exhausted before their shrinkage effects could be recorded 

 by deformation in a solid form. Little more than the shrinkage 

 effects of cooling after solidification could be registered in diastrophic 

 features. On the other hand, if the earth were built up largely by 

 accretions in a solid state, especially if these were minute and laid 

 down in random fashion, a much larger proportion of the potential 

 resources of shrinkage would be registered in fixed solid forms. More- 

 over, this would take place while the formative processes were in 

 progress, and would thus be subject to their influence. The deforma- 

 tions under the two hypotheses, therefore, differ widely in amount and 

 in kind, as also in the stages at which they were chiefly effected. 



A previous examination of the great features of the earth had seemed 

 to reveal an amount of deformation much greater than has usually been 

 assigned under the molten theory and somewhat greater also than had 



^With the permission of the President of the Institution, some of the preliminai-y results of 

 these studies have been published in the Journal of Geology, constituting articles x, xi, xii, anfl 

 XIII (1920) of a series of papers entitled "Diastrophism and the Formative Processes." 



