Theories oith- Earth s Origin — Uphnm. 215 
lack of sufficient compression in the central parts to give the 
requisite heat, and (2) by the time required for this central heat 
to move out to zones of less pressure, where it would suffice to 
melt the more fusible constituents. But, once begun, it is sup- 
posed to have gradually increased in actual and in relative im- 
portance until it reached its climax. This obviously came much 
later than the climax of growth, for it was dependent on the 
growth to give the increased compression from which arose the 
central heat on which the vulcanism depended. * * * 
The formations of this period of volcanic dominance, with 
very subordinate clastic accompaniment, are regarded as consti- 
tuting the Archean complex, though perhaps only the later por- 
tions of the great volcanic series are represented by the known 
Archean. 
To give a satisfactory statement of Professor Cham- 
berlin's exceedingly interesting and elaborate theory has 
thtis required very large quotation from his recent publica- 
tion of it. Only by such direct presentation of his work in 
his own words could justice be done to this new nebular 
theory, to which this eminent glacialist was primarily led 
by his endeavors to explain the causes of the Ice Age, 
and of its several waxing and waning stages, by periodic 
changes in the content of carbon dioxide in the atmosphere. 
Having been an assistant under his direction on the United 
States (jeological Stirvey during seven years in my work 
on the Glacial Lake Agassiz, it is with great pleasure and 
pride that I can claim for him and for America the dis- 
tinguished honor of having developed this great theory of 
the origin of the earth. It will certainly introduce into 
geology and geophysics many new and fruitful methods 
of observation and research. Indeed, nearly all the great 
fields of theoretical geology now require renewed investi- 
gation, by which the planetesimal hypothesis shall be 
tested. 
An earlier address by Professor Chamberliii, partially 
setting forth his studies in this direction, was given before 
the Geological Society of America, at its fifteenth annual 
meeting, in Washington, D. C., on January i. 1903, entitled 
"Origin of Ocean Basins on the Planetesimal Hypothesis ;" 
but only a very brief abstract or note of this address was 
published.* 
* Bulletin, Geol. Soc. America, vol. xiv. p. 548, March, litm; and Am- 
tiEOLoiJisT, vi)l. xxxil, p. 14, July, 1903. 
