With certain qualifications, a summary of the leading events that have left their impress on the region is as follows:
4. Surface eruption of quartz-porphyry, rhyolite, and andesite.
7. Submergence, deposition of Cambrian formations; slight oscillations during their deposition; reduction of land to baselevel.
8. Eastward tilting and deposition of Martinsburg shale; oscillations during later Paleozoic time.
9. Uplift, post-Carboniferous deformation and erosion.
10. Depression and Newark deposition; diabase intrusion.
11. Uplift, Newark deformation; and erosion to Catoctin baselevel.
12. Depression and deposition of Potomac, Magothy, and Severn.
13. Uplift southwestward and erosion to baselevel.
14. Uplift, warping and degradation to Tertiary baselevel; deposition of Pamunkey and Chesapeake.
15. Depression and deposition of Lafayette.
16. Uplift and erosion to lower Tertiary baselevel.
17. Uplift, warping and erosion to Pleistocene baselevel; deposition of high-level Columbia.
18. Uplift and erosion to lower Pleistocene baselevel; deposition of low-level Columbia.
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.