14 The American Geologist. Jl,l> L90a 
A little southeast of where the esker crosses the railroad is 
a high isolated hill of unstratified gravel and cobbles, while a 
mile or so to the northwest are a number of drumlin like hills 
running: into true drumlins still further to the northwest. 
THE ORIGIN OF OCEAN BASINS ON THE 
PLANETESSIMAL HYPOTHESIS.* 
By T. C. Cha.miieki.ix, Chicago, 111. 
The Planetessimal Hypothesis of the origin of the solar 
system differs fundamentally from the Laplacian and other 
gaseous hypotheses, and from the meteoroidal hypothesis as set 
forth by Lockyer and Darwin. These latter assign the ex- 
tension of the parent nebula to the opposed movements, col- 
lisions and rebounds of the constituent molecules or meteor- 
oids. The former assigns it to concurrent orbital movement. 
In the gaseous and meteoroidal hypotheses (as usually un- 
derstood) the aggregation is the simple work of gravity 
following a reduction of the oscillatory and colliding ac- 
tion. In the planetessimal hypothesis the aggregation is 
individual and relatively slow. In the gaseous hypothesis 
the temperatures are necessarily very high, and the planets 
are formed by detachments. In the meteoroidal concep- 
tion of George Darwin, the conditions are practically 
the same, and in that of Lockyer they differ rather in 
degree and in detail than in essence. In the planetessimal con- 
ception the planets grew up separately by innumerable accre- 
tions of infinitessimal planetoids (planetessimals ) and the ex- 
ternal temperatures were not necessarily high, since the orbits 
of the planetessimals were normally direct and concurrent and 
the aggregation came about by overtakes in contradistinction to 
opposed collisions, and the frequency of these was limited by 
the concurrent direction of orbital movement. 
The purpose of the paper is to outline the hypothetical ori- 
gin of the ocean basins under the planetessimal theory, to set 
forth the simple self-selecting process by which they were per- 
petuated and deepened, and the connection of this was the dy- 
namics of deformation. (30 minutes.) 
* Abstract of a paper presented at the Washington (1902) meeting G. S. A. 
