81 
to their present positions, as they overlie undisturbed strati- 
fied sands and clays, which would have been broken up and 
carried away by glaciers or currents of water, moving with 
sufficient velocity to transport these blocks. Hence they 
must have been floated from the Canadian highlands, the 
place of origin of most of them, by ‘cebergs. 
This epoch of the Drift period I have therefore termed the 
Iceberg Epoch. During this epoch the submergence of the 
land in the interior of the continent, was greater than in the 
epoch of the deposition of the Champlain and Erie clays, and 
all the area north of the Ohio was covered with water up to 
a height of over 500 feet above Lake Erie, or 1100 feet above 
the Ocean level. The highlands of south-eastern Ohio, and 
most of the country South of the Ohio river, were not covered 
by this flood, and now bear no Drift deposit of any kind. 
Tracing out the line of ancient water-surface, we find that 
the depression was greater toward the North, so that the 
Alleghanies and their foot-hills, and also a wide area of com- 
paratively low country in the Southern states, formed not 
only a shore, but a continental limit to the great interior ice- 
berg-ridden sea of the later Drift Epoch. 
In the western reaches of this sea, which was of fresh 
water, in the later centuries of its existence, was deposited 
the Lées or “‘ Bluff” which I have elsewhere designated as the 
later lacustrine, non-glacial Drift. During the deposition of 
the Lées, the interior sea was already narrowing and growing 
shallower by the cutting down of its outlets, or by continen- 
tal elevation or both. The descent of the water-level, and 
decrease of water-surface, have been going on perhaps con- 
stantly but not uniformly, to the present time, when the area 
of the great lakes is the insignificant 85,000 square miles it 
now is. In the descent of the water-level, retarded at certain 
periods, Terraces and beach lines were formed at various 
places by the shore waves. With these the history ends. 
This then is the classification I would suggest of the Drift 
deposits, as they occur in the valley of the Mississippi, pre- 
mising that here as in other geological periods, the column is 
nowhere absolutely complete. 
