140 
FOURTEENTH REPORT. 
Tylor* thought that the ice-mantle lowered the sea GOO feet. 
IJeltt accepted Hartt and Agassi// belief in glaciation in South 
America nearly to the equator, contemplated the large amount of evi- 
dence indicating a low level of the ocean during the Glacial Epoch and 
thought that Tylor's GOO feet would have to be increased to 1,000. 
Upham considered the ocean surface as about 115.000,000 square 
miles and the ice areas of Europe and North America as 2,000,000 and 
1.000,000 respectively, and put the thickness of the ice at a half or 
two-thirds of a mile, perhaps even a mile. This would mean between 
218 and 219 feet of ocean lowering for one mile of ice over the glaciated 
area. Conversely the melting of this amount of ice would raise the 
general level a like amount. Some other cause would have to terminate 
the Glacial Epoch, the ice-water being merely an incident. 
As suggested above, under isostasy the glacial ice must be conceived 
to have depressed its area, offsetting more or less the lowering of sea- 
level by abstraction, and conversely upon its melting the return move- 
ment must be reckoned with. This probable glacial lowering and post- 
glacial elevation cannot apply to regions lightly or not at all glaciated 
and cannot therefore alter the main conditions of the problem. 
The melting of the glaciers from some cause other than change of 
altitude above the sea, and the consequent return of the ice-water to 
the ocean is not adequate to account for the increase of ocean volume 
which is demanded by the observed degree of submergence. For the 
oceans, with their area thrice greater than the land, to be raised a 
mile with reference to the land all the continents would have to yield 
the water of ice-mantles averaging three miles in thickness and for 
even this to be possible there must have been no isostatic depression of 
the lands under the load. 
conclusion. 
We have now taken a fairly comprehensive view of the causes which 
have heretofore been suggested in explanation of the encroachment of 
the sea upon the land in Postglacial time. It has been possible, I think, 
to eliminate, one by one, all excepting the suggestion which was ventured 
that there might be such a thing as meteoric or planetessimal water, 
if the exclusion of one after another of the possible alternatives were 
less positive the case would be different, but nothing else seems to offer 
even a reasonable approximation to an explanation of the phenomena 
which await one. There is nothing inherently impossible in the sugges- 
tion that planetessimals gathered by the earth may once in a while in- 
clude water enough to make considerable difference with the balance 
of things on the earth. Neither is there any need for denying that such 
an event or several such events may have occurred even as recently as 
Pleistocene time or the present day for that matter. It is by no means 
necessary to make such a conception dependent upon the acceptance of 
all aspects of the planetessimal hypothesis as at present developed. The 
arrival of cosmic materials upon the earth is a matter of common obser- 
vation. The ability of water to traverse the interplanetary vacuum 
can scarcely be denied albeit that it may be advantageous to call upon 
*Tylor, Alfred, Geological Mag. vol. ix, p. 392. 
fBelt, Thomas, “The Naturalist in Nicaragua,” London, 1874. 
