PREVIOUS WORK IN THE REGION. 433 



Previous writers on the geology of the coastal plain region of Virginia 

 and Maryland comprise Conrad, W. B. Rogers, McGee, Fontaine, Uhler, and 

 W. B. Clark, together with a few others whose observations have been less 

 extended. 



It does not seem desirable at present to give an exhaustive account of the 

 contributions of these observers, and only a brief sketch is here offered : The 

 formation now known as Potomac was described by Rogers* in Virginia, 

 and McGee f and Fontaine X have studied it both in Virginia and Maryland. 

 The extension of the Cretaceous through the western shore of Maryland was 

 established by W. B. Clark, § and Uhler || has also described some of its 

 features. The Eocene and Miocene formations have been considered at 

 greater or less length in the paleontologic writings of Conrad, by Rogers in 

 reports on geological surveys of Virginia, and in parts of eastern Maryland 

 by Uhler in the paper above referred to. 



The Appomattox south of the Fredericksburg region was differentiated by 

 McGee,^ and to this observer we are also indebted for the separation and 

 study of the Columbia formation.** 



While these various investigations have afforded a most valuable basis for 

 the elucidation of coastal plain geology, especially in certain type areas 

 where the relations are more obvious, the greater part of the region is left 

 involved in geologic questions of very great intricacy. This is especially 

 the case in the many districts in which there are complex overlap relations, 

 intergradations and similarity of deposits, weathering, shore phenomena and 

 inter-geologic terracings, which, in soft materials with unsatisfactory ex- 

 posures, are often exceedingly puzzling. 



During the past two years the writer has been engaged in almost continu- 

 ous field-work in this region ; and in this memoir it is proposed to give a 

 brief general abstract of the more noteworthy results, as a preliminary 

 contribution to coastal plain geology. The investigation is still actively in 

 progress, and more extensive reports of results and methods will appear 

 later. 



The Formations. 



THE GEOLOGIC COLUMN. 



The components of the geologic column of the coastal plain region of 

 Virginia and Maryland are as follows : 



* Report of Progress of Geological Survey of Virginia for 1840, chap. III. 



t" Three Formations of the Middle Atlantic Slope:" Am. Jour, aci., 3d ser., vol. XXXV, 1888, 

 pp. 121-143. 



X " The Potomac or Younger Mesozoic Flora : " Monographs U. S. Geol. Survey, vol. XV, 1889, pp. 

 1-62. 



g Johns Hopkins University Circulars, vol. 8, no. 69, 1889, pp. 20-21. 



II Proc. Maryland Acad. Science, vol. 1, 1888, pp. 11 3:!, 45-98. 



i Loo. cit , pp. 328-330. 



** Loc. cit., pp. 367-388, 448-466 ; and in " The Geology of the head of Chesapeake Bay : " 7th Annual 

 Report of the Director U. S. Geol. Survey, 1885-86, pp. 537-646. 



