MICHIGAN ACADEMY OF SCIENCE. 
137 
Without pretending to anything minute in such a matter we may get 
some idea of the probable values of such movements by viewing the rela- 
tions of the masses involved. If (lie specific gravity of the continental 
masses is three times that of water the land will tend to rise one-third of 
any theoretical rise of the ocean due to increase of volume. Supposing 
perfect adjustment, a mile of water laid on over the oceans would give 
1,760 feet of compensatory, isostatic, elevation of the land. If the 
density of continental materials be placed at only 2.75 fhe result is 
somewhat greater, 1,920 feet. There is a certain usefulness in such 
figures, they give the idea that even with imperfect isostasy the com- 
pensatory elevations would very likely be of no mean amplitude and 
cannot at all be disregarded. There is good opportunity for thought 
here, in contemplating a possible relationship between the changes on 
the part of the sea and the Champlain depression and Terrace reeleva- 
tion on the part of the land. 
Now, we may well ask, what are the possible causes of change in 
the volume of the oceans? And how effectively do they till the place 
that we have been preparing for that great cause that shall adequately 
explain the phenomena under consideration? There are five or six, as 
far as I can learn, of which Suess considers two, the formation of new 
mineral silicates lessening, and volcanic eruptions increasing the vol- 
ume. The first of these may of course be omitted altogether in searching 
for causes of rise of ocean level ; the second cannot possibly play an 
important role. Most of the water emitted by volcanoes is only that 
which has collected in craters or seeped in through fissures in the rocks. 
There are other causes, that Suess does not mention, which may 
well be carefully reviewed. Heat, both solar and terrestrial, might 
play an important part and glaciation also. Let us take first solar 
heat, or rather, fluctuations in it, as a possible cause of changes of 
ocean volume. 
Variation in orbital eccentricity, while changing the character of our 
seasons, cannot alter the amount of heat annually received from the 
sun; it has however, before now, been attempted to account for the 
Glacial Epoch by postulating changes in the amount of heat emitted by 
the sun, and in asmuch as more heat absorbed would convert more 
oceanic water into vapor and a lessening of that heat would permit re- 
condensation, this factor, while it cannot be given rank as an established 
true cause still deserves mention as a possible theoretical cause of 
change of ocean volume. The Glacial Epoch being accepted as a time 
of land-elevation or sea-level depression, and its termination being 
coincident with the reversal of that condition, we should have to at- 
tribute the glaciation to heat and its disappearance to chilling because 
the sun radiated less heat to be absorbed by the earth. This paradox, 
however, might not be as improbable as it sounds, and Professor Frank- 
land,* in 1864, presented considerable argument to prove a closely re- 
lated proposition, namely, that the real cause of the Glacial Epoch was 
an oceanic temperature, due to terrestrial heat, higher than that of 
the present day. A similar idea was emphasized by Professor Tyndall. 
Frankland did not overlook this important difference between the two 
ideas, (solar heat and terrestrial) that warm oceans need not neces- 
*Frankland, E., “On the Physical Cause of the Glacial Epoch.” (The London, Edinburgh and 
Dublin) Philosophical Mag. and Jour, of Sci., Ser. 4, vol. 27, 1864, pp. 321-341. 
