730 NATURAL HISTORY MISCELLANY. 
nated as the later lacustrine, non-glacial drift. During the depo- 
sition of the Loess the interior sea was already narrowing and 
growing shallower by the cutting down of its outlet or by conti- 
nental elevation, or both. The descent of the water-level and 
decrease of water-surface have been going on perhaps constantly, 
but not uniformly, to the present time, when the area of the great 
lakes is the insignificant eighty-five thousand square miles it now is. 
In the descent of the water-level, retarded at certain periods, ter- 
races and beach lines were formed at various places by the shore 
waves. With these history begins. This then is the classification 
I would suggest of the drift deposits as they occur in the valley 
of the Mississippi, premising that here, as in other geological pe- 
riods, the column is nowhere absolutely complete : — 
PERIOD. | EPOCHS. STRATA. | NOTES. 
Terraces, Sand and gravel beaches with logs, 
Beaches, $ leaves, and fresh-water shells. Löess 
Löess. with fresh-water and iand-shells 
Iceberg Boulders, gravel, sand, and clay, 
Terrace. jJ Drift, ; drifted logs, elephant and mastodon 
dess. eeth and bones. 
Soil-peat with mosses, leaves, logs, 
Forest stumps, branches, and standing trees, 
Quaternary. } | Bed: mostly red cedar. Elephas, mastodon, 
Castoroides, etc. 
Laminated clays with sheets of grav- 
Erie el, occasional rounded and scratched 
Clays. soem boulders, many angular pieces 
ofn lyi . 
U diea" 3 t nderlying rocks i 
i Local beds of boulders and rare 
preg ; boulder clay resting on the glaciated 
j surface. 
From the above table it will be seen that the remains of ele- 
phant, mastodon, and the gigantic beaver, occur in the forest-bed 
and in all the succeeding drift deposits. It should also be said 
that they are found in still greater abundance in peat-bogs and al- 
luvial deposits which belong to the present epoch. We have seen 
that the submergence of the later drift epoch, though so wide- 
spread, left a large part of the area lying between the Mississippi 
and Atlantic uncovered. This area the elephant, mastodon, great 
beaver, eté., inhabited during the continuance of the flood that 
covered the forest bed. From this retreat they issued with the 
subsidence of the water, following the retreating shore-line, till 
they occupied all the region now exposed about the great lakes. 
