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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3d. At this period the continent must have been several hundred feet
higher than now, as is proved by the deeply excavated channels of the
Hbdson, Mississippi, Columbia, Golden Gate, etc., which could never
have been cut by the streams that now occupy them, unless when flowing
with greater rapidity and at a lower level than they now do. Similar
submarine troughs lead out from the mouths of the Chesapeake and
Delaware Bays, showing that the Susquehana, Potomac, York and James
rivers were once branches of a single stream, which, like the Schuylkill,
had its mouth face to the east of the present coast line.
The depth of the trough of the Hudson is not known, but it is plainly
a channel of erosion, now submerged and become an arm of the sea.
This channel is marked on the sea bottom for a long distance from the
coast and far beyond a point where the present river could exert any
erosive action, and hence it is a record of a period when the Atlantic
coast was several hundred feet higher than now (J. D. Dana.)
The lower Mississippi gives unmistakable evidence of being-if one
may be permitted the paradox-a half-drowned river; that is, its old
channel is deeply submerged and silted up, so that the "Father of Waters," lifted above the walls that formerly restrained him, now wanders
lawless and ungovernable, whither he will in the broad valley.
4th. The Ice period-a period of continental elevation and of active
erosion-was followed by a water period, when the continent was depressed five hundred feet or more below its present level; when the climate was much warmer than before; when the glaciers retreated northward and were gradually replaced, in the basin of the great lakes, by an
inland sea of fresh water. In this period were deposited the fine, laminated clays (Erie clays) which cover so much of the glacial surface in
the interior of the continent, and the " Champlain clays," that hold the
same relative position in the Atlantic slope. The Champlain clays contain abundant marine, arctic shells, but the Erie clays are not certainlyknown to contain any fossils except floated trunks, branches and leaves
of corniferous trees-pines and spruces-now growing on the northern
part of the continent.
5th. After the deposition of the Erie clays, sand, gravel and boulders
in large quantities were transported from the region north of the lakes,
and spread over a wide area south of them. That these materials were
not carried by currents of water or glaciers is Certain; as either of these
transporting agents would have torn up the Erie clays, which now form
an unbroken sheet beneath them. We are therefore forced to the conclusion that they were floated to their resting places, and that by icebergs. Icebergs are always formed by the rupture of the end of a glacier protruded into the sea; and they always carry boulders, gravel and
sand from their places of origin, and deposit them when they melt.
When our lake-basin glaciers had retreated to the highlands north of