Nczv Hypothesis of Earth-Origin. — PaircJiild. 95 
science, and as one of the glories of American geology. This 
is true even if the new hypothesis should not wholly stand. 
The critical application of accepted principles of physics to 
the nebular hypothesis by Professor Chamberlin has revealed 
its weakness even under direct attack. The planetesimal hy- 
pothesis which he has formulated as a substitute seems much 
better to explain both the astronomical and geological phe- 
nomena. It may not be immediately and universally accepted, 
as it destroys the present foundation of many geological the- 
ories, and because the leaders in science are committed to the 
old ideas ; and in all its claims it may not be true. But its 
main postulate, that the globe was formed by accretion of cold 
matter, will probably stand. 
The purpose of this writing is not to make an extended 
argument for the new hypothesis* nor to discuss its relations to 
celestial physics nor even to the solar system, but to indicate 
its bearings on several problems in geology and very briefly to 
show how these problems are simplified by the new conception. 
It is predicted that under the stimulus of the new thought so 
many changes will be made in our views of geologic processes 
that the science of geology will be rejuvenated, as its theoretic 
or philosophic advance has been seriously retarded by its de- 
pendence on a false conception of earth genesis. 
Comparison of the Nebular and Planetesimal Hypotheses. 
The old hypothesis assumes the existence of a mass of 
incandescent vapor, with or without a nucleus, which by con- 
densation and rotation was differentiated into successive rings ; 
the latter being eventually gathered up into the planets zvhiU 
still retaining intense heat. From this postulate there neces- 
sarily follows the conception of a cooling earth ; and hypogeic 
geology has been founded on the idea of crustal solidification 
on a molten globe. The new hypothesis holds that the dissem- 
inated planet-forming matter Jiad lost its heat while yet exist- 
existing in the loose form, as rings or zones or wisps of the 
parent nebula, and that the globular planets were formed by 
the slozv aceretion or infalling of cold, discrete bodies or par- 
ticles ("planetesimals"). 
* The full presentation of this hypothesis wilt be given in a new text-book 
of geology by T. C. Chamherlin and R. D. Salisbury. 
