MICHIGAN ACADEMY OF SCIENCE. 
1 23 
There are two or three factors to be taken into consideration in this 
connection. In the neighborhood of severe glaciation Ihe borders of 
the North Atlantic must have received heavy blankets of sediment and 
elsewhere as well, where lliese drowned river mouths are found, tlrey 
are in precisely the best situations for heavy sedimentation. An excep- 
tion may be noted in the southeast part of the Bay of Biscay, where 
there is now no very large river to carry down silt, and it may be of 
some significance that here we find a 9,000 foot depth. There is also, 
however, the possibility that some of this 9,000 feet represents isostatic 
depression by the Pyrenees mountains close by. 
The sediment of the Congo appears, according to Buchanan, to be 
carried northward and deposited along the bank rather than out over 
the old channel. 
Again, the figures for North America, aside from the Antillean region 
run lower than those for Europe and Africa and it may be that the 
heavy load of ice which the northern part carried caused it to stand 
at a lower level than the lands which were glaciated lightly or not at 
all, so that the rivers sooner reached their baselevels of erosion. By the 
same influence the relief when the ice melted would permit more of that 
elevation which corresponds to the Terrace epoch and bring the drowned 
vales still nearer the surface of the sea. But regardless of these finer 
and more debatable points, the submergence which marked the close of 
the Glacial epoch runs into figures which, on the average, may be not 
unfairly expressed as a mile or more. (The matter of correlation will 
receive attention as we proceed.) 
OTHER GEOLOGICAL EVIDENCE. 
Sedimentary deposits washed down by the Mississippi to the Gulf 
region, the so-called “modified” or stratified drift, prompted Hilgard* 
to assign to the upper part of the Mississippi valley a former elevation 
above sea level of 4,000 to 5,000 feet. 
He also inferred, from the character of the later Tertiary deposits 
in the gulf region that prior to the Glacial or Drift epoch the Gulf of 
Mexico was nearly or quite isolated from the Atlantic ocean, probably 
by elevation of the northern borders of Ihe Caribbean sea, so that it was 
freshened by the inflow from the land. This inference receives strong 
corroboration from another quarter, as we shall have occasion to re- 
mark in connection with the distribution of land and freshwater shells 
and Crustacea. 
Falconerf reviewing the various phases of this antillean elevation, 
dates the high emergence of the islands from about the beginning of the 
Tertiary and thinks it terminated in sinking during the Pleistocene 
period. 
Passing southward to Brazil. Hartti contemplates the distribution of 
the so-called “drift” between Porto Novo and Porto das Caixas and at 
Bahia and considers that when it was deposited Ihe land stood at a 
higher level than now. The time of this “drift” deposit was placed by 
*Hilgard, Eugene W., “The Age and Origin of the Lafayette Formation.'’ Am. Jour. Sci., Ser. 3, 
vol . xliii, 1892, pp. 389-402. 
tFalconer, J. it., “The Evolution of the Antilles.” Scottish Geographic Magazine, vol. xviii, 1902, 
pp. 369-370. 
JHartt, Ch. Fred, "Geology 
and Physical Geography of Brazil.” 
1870. 
