MICHIGAN ACADEMY OF SCIENCE. 
135 
questionable, might be regarded as tending to increase this attraction; 
and it would seem that an increased relief of 1 lie lands above the sea 
must surely also increase it. While all such considerations as this 
ought to be kept well in mind in any attempt at an impartial investiga- 
tion, it is not apparent how this element of gravitational displacement 
can affect the problem of rise of ocean level. The most that would have 
to be considered would be fluctuations' in the amount of it and if we 
had to take the whole it cannot amount to much. 
Another idea coming under the head of displacement is the possible 
filling of ocean areas with extraneous material. Suppose we accept 
Professor Chamberlin’s planetessimal hypothesis and the earth receives 
a marked addition of mass in the form of planetessimal or meteoric 
matter. There might be a readjustment of the relations of the land 
to the sea whether the increment happened to alight mainly on the 
oceanic areas or on the land. If it partially filled up an ocean bed, the 
newly acquired mass, by depressing its own area and causing a com- 
pensatory rise elsewhere, might partially offset its own first effect as a 
raiser of sea level. No such large accession of mass is recognizable at 
the present time. We cannot too lightly throw aside anything that even 
resembles a possibility and geological literature is not wholly lacking 
in suggestions of this very kind, but it does not seem that we need 
hesitate to exclude this kind of displacement as an explanation of the 
change of level to the extent of thousands of feet at the period in ques- 
tion, with just one possible exception. I am not aware that any particu- 
lar restrictions have been imposed upon the chemical composition of the 
planetessimals. If the earth has been built up by accretions of mass 
from interplanetary space there does not seem to be any good reason 
why we must not suppose that the water came the same way as the other 
materials. And if it did, when was that? And just how much of it 
came at any one time? How are we to exclude such a possibility? 
That will have to be taken up again in a moment. 
There are two theories of marine oscillation which require mention. 
Croll* in 1875 believed in alternate north and south glaciations with 
shifting of the earth’s center of gravity and pole-to-pole oscillation of 
the sea, high level of the ocean coinciding with glaciation. There are 
two apparently fatal objections to this theory, at least in so far as it 
applies to ocean level ; first, there is abundant evidence that the glacia- 
tion of the northern lands coincided not with a high-water but with a 
low-water phase; and second, in the course of pole-to-pole oscillations 
of the sea the tropical zone must be expected to be a region of minimum 
vertical movement. The facts are that the measures of the drowning in 
the tropical zone are well up to the general standard. 
Suess’f theory of marine oscillation is that from some cause yet to 
be assigned there are alternate accumulations of water at the poles and 
at the equator. This might be connected with ice-attraction with 
bipolar glaciation but that explanation is not adequate for the large 
values obtained. Since the figures of both the hydrosphere and the 
lithosphere are dependent upon the rate of rotation, and we can find 
no indications of any considerable change in the rate,! it is very hard 
*Croll, James, “Climate and Time in their Geological Relations.” 1875. 
tSuess, Eduard, “The Face of the Earth,” Eng. trails, vol. ii, p. 563. 
jChamberlin, T. C., “Former Rates of the Earth’s Rotation” etc., In “Tidal and Other Problems,”' 
Carnegie Institution, 1909. 
