MARYLAND GEOLOGICAL SURVEY 203

trough to a depth of nearly three miles, was raised in a series of folds,
transforming the former sea into a great mountain chain, although
perhaps of no greater, if as great, proportions as it has to-day. From
its first appearance above the waters, this mountain chain has been
continually preyed upon by rain, wind, frosts and streams, with the
result that the greater proportion of its bulk is to-day stretched out
along our coastal border. Its growth was gradual—at least not the
product of a sudden revolution—so that the period of its greatest ele-
vation can be with difficulty determined. As the result of the ele-
vation of the Appalachians into the great mountainous area the sea
was crowded out of its position in the eastern interior portion of our
continent; but early in Mesozoic time, already during the Triassic
period, a long, narrow trough extended across Maryland near the
eastern edge of the mountainous district, in what is to-day the Fred-
erick valley, and in this trough was deposited a great thickness of red
sandstones and shales (Newark formation), cut through and inter-
bedded with flows of eruptive rock (Diabase). Toward the middle of
Mesozoic time there was a decided continental elevation, which drained
the interior trough, while the deposits of this period were doubtless
laid down far to the eastward of the present coast-line.

Later in Mesozoic time, probably near the close of the Jurassic
period, there was a marked depression of the continent along its
eastern border which brought the sea to and beyond the present west-
ern margin of the Coastal Plain. There is good evidence that this
eastward tilting of the continent was not at right angles to the present
oceanic border or persistent for any great length of time in the same
direction, as is shown by the irregular transgression of the several
formations of the Cretaceous period. Broad reaches of shallow and
brackish waters bordered the coast during the later Jurassic and early
Cretaceous periods, and shore currents distributed the material brought
to the sea by the rivers. Continuous depression, however, did not
take place during this period; the deposits were several times raised
and subjected to denuding agencies. At the close of the lower Creta-
ceous a pronounced erosion interval occurred prior to the depression,
which brought in the marked marine conditions of upper Cretaceous