18. Uplift and erosion to lower Pleistocene baselevel; deposition of
low-level Columbia.

19. Uplift and present erosion.

Along the Coastal plain reduction to baselevel was followed by
depression and deposition of Lafayette gravels; elevation followed and
erosion of minor baselevels; second depression followed and deposition
of Columbia gravels; again comes elevation and excavation of narrow
valleys; then depression and deposition of low-level Columbia; last,
elevation and channeling, which is proceeding at present. Along the
Catoctin Belt denudation to baselevel was followed by depression and
deposition of gravels; elevation followed and erosion of minor
baselevels among the softer rocks; second depression followed, with
possible gravel deposits; elevation came next with excavation of broad
bottoms; last, elevation and channeling, at present in progress.

The general structure of the Catoctin Belt is anticlinal. On its core
appear the oldest rocks; on its borders, those of medium age; and in
adjacent provinces the younger rocks. In the location of its system of
faulting, also, it faithfully follows the Appalachian law that faults
lie upon the steep side of anticlines.

After the initial location of the folds along these lines, compression
and deformation continued. Yielding took place in the different rocks
according to their constitution.

Into this system of folds the drainage lines carved their way. On the
anticlines were developed the chief streams, and the synclines were