Part I. Report of progress in 1869, by J. S. Newberry, chief geologist. Part II. Report of progress in the second district, by E. B. Andrews, assist. geologist. Part III. Report on geology of Montgomery County, by Edward Orton, assist. geologist.

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one great inland sea. Even when the ridge which ran through the city
of Cleveland was formed, the water of Lake Erie stood one hundred feet
higher than now, and all our great lakes formed a single sheet of water
broken only by a few scattered islands. The depression or the water
level was apparently caused by the cutting down of the outlets. That
process is perhaps going on as rapidly now as ever. The last hundred
feet of depression of the water surface, we know, has been effected by
the cutting down of the Niagara barrier, and every day now must witness something removed from it by the torrent that rushes over it.
Larger lakes than those on which we now pride ourselves have been
emptied, in the western part of our country, by thus cutting down of
the gorges of the Columbia, Klamoth and Sacramento, and it is evident
that, if present causes continue to operate, at no yery remote period,
geologically speaking, all our lake basins will be converted into vallies
traversed by rivers.
9th. In the retreat of the shore line from the contraction of the water
surface to its present area, every part of the slope between the present
and highest ancient lake levels-i. e., all within a vertical height of three
hundred feet-must have been submitted to the action of the shore
waves, rain and rivers; by which these loose materials were rolled,
ground, sorted and shifted until little was left of the original bedding.
The fine materials-clay and sand-must have been washed out and carried farther and still farther into the/lake basin, to form, in short, the
upper sandy layers of the Drift.
In this " modified Drift," especially in the old river deltas, the remains
of elephant and mastodon are frequently found; never, so far as yet
known, in the older, true Drift.
I have said that the erratic blocks, of northern origin, which stud the
surface over so large a space south of the lakes, were the last of the
Drift deposits. That the lake ridges are of later date is proven by the
fact that, while the ridges often traverse surfaces strewed with boulders,
none of these are ever found on them.
In all the changes of elevation and climate which the valley of the
Mississippi experienced during the Drift period, its general structure
and main topographical features remained the same; yet the character
of its surface suffered very important modifications, and such as deeply
affected its fitness for human occupation. Going back to the later Tertiary ages for a starting point, we find the following sequence of events
recorded:
a. In the Miocene and Pliocene epochs: The continent several hundred feet lower than now; the ocean reaching to, Louisvillb and Iowa;
great lakes in the country bordering the Upper Missouri; a sub-tropical
climate prevailing over the lake region; the climate of Greenland and