MARYLAND GEOLOGICAL SURVEY 123 



which fall below 500 feet are represented as if they were fjords of the 

 Lafayette sea. It will be noticed that the gravel deposits near Freder- 

 ick, if they belong to the Lafayette formation, are the only recognized 

 remnants in western Maryland. All the other materials which must have 

 been deposited in the Appalachian valleys, if the geography was approxi- 

 mately as represented, appear to have since been removed by erosion. If 

 the shore line of the Lafayette sea stood at approximately 500 feet, it falls 

 into line with what we know regarding the altitude of the deposits in the 

 eastern part of the State and is in harmony with the gravel-covered ter- 

 races lying against Bull Mountain at the height of 500 feet in Virginia, 

 described by Keith in his " Geology of the Catoctin Belt." 



It has been shown elsewhere by Dr. Cleveland Abbe, Jr., 10 that the rivers 

 of the Piedmont Plateau are superimposed. It is possible that these un- 

 adjusted courses so common near Baltimore were conditioned by the sur- 

 ficial cover of Lafayette. After the deposition of the Lafayette forma- 

 tion, the land was raised above ocean-level and subjected to an interval 

 of erosion which was probably of longer duration than the later ones 

 which separated the other surficial deposits of the series. The salient 

 features of the Coastal Plain topography were outlined at this time 

 although it is doubtful if they received their full strength or final touches 

 before the post-Talbot uplift. It is evident that the valleys of the Po- 

 tomac, Patuxent, and other large rivers as well as that of Chesapeake 

 Bay existed, since the Sunderland formation, which was deposited when 

 this topography was submerged, slopes toward all these depressions. But 

 it is not probable that these gorges were cut as deeply as they are now for 

 the Sunderland formation nowhere shows a tendency to develop a thick- 

 ness sufficient to fill such a valley. It rather gives the impression of a 

 thin deposit which veneered wide, shallow depressions. The anomalous 

 course pursued by the Susquehanna after leaving the Piedmont, in turn- 

 ing south along the western margin of the Coastal Plain instead of con- 

 tinuing a direct course to the ocean, has arrested the attention of many 

 geologists who have worked in this region. McGee thought this curious 



10 A General Report on the Physiography of Maryland. Cleveland Abbe, Jr. 

 Md. Weather Service, vol. i, pp. 37-216, 1899. 



