[Footnote 6: The name "Catoctin Belt" is applied to this region because it is separated by Catoctin Mountain from the Piedmont plain as a geographic unit more distinctly than in any other area, and because its geological unity is completed by Catoctin more fully and compactly than elsewhere.] In this important work the Catoctin Belt is shown to be an epitome of the leading events of geologic history in the Appalachian region. It contains the earliest formations whose original character can be certified; it contains almost the latest known formations; and the record is unusually full, with the exception of the later Paleozoic rocks. Its structures embrace nearly every known type of deformation. It furnishes examples of every process of erosion, of topography derived from rocks of nearly every variety of composition, and of topography derived from all types of structure except the flat plateau type. In the recurrence of its main geographic features from pre-Cambrian time till the present day it furnishes a remarkable and unique example of the permanence of continental form. With certain qualifications, a summary of the leading events that have left their impress on the region is as follows: 1. Surface eruption of diabase. 2. Injection of granite. 3. Erosion. 4. Surface eruption of quartz-porphyry, rhyolite, and andesite. 5. Surface eruption of diabase. 6. Erosion. 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. 19. Uplift and present erosion.