114 THE PLIOCENE AND PLEISTOCENE DEPOSITS OF MARYLAND 



ton and Charlotte Hall, the plain slopes toward the southeast at the aver- 

 age rate of 5.5 feet per mile, while from Woodlawn at the head of the 

 Bay to Charlotte Hall, it slopes at the average rate of 3.1 feet per mile. 

 Other intermediate averages may be easily ascertained by consulting the 

 diagram. Thus the plain surface and the seaward slope of the Lafay- 

 ette terrace are demonstrated. 



The second and third requirements in establishing an analogy between 

 this plain and the present subaqueous terrace is the presence of a scarp 

 and a datum line. As both of these have been destroyed by erosion, the 

 fourth and last requisite will be considered. This specifies that the 

 Lafayette deposit should show conclusive evidence of its original con- 

 tinuity. There seems to be no reasonable doubt for accepting this con- 

 clusion. Geologists who have worked on this deposit have been impressed 

 by the continuity of this formation and with the fact that the various 

 outliers were at one time united in a continuous deposit. McG-ee traced 

 the Lafayette up to Fredericksburg. Lewis recognized the isolated rem- 

 nants of Lafayette gravel lying on the hilltops near Philadelphia and pro- 

 posed for them the name of Bryn Mawr gravels, thereby indicating that 

 they were one and the same formation. Finally, Darton followed the 

 Lafayette northward from Fredericksburg and showed that the outliers 

 of Bryn Mawr in the vicinity of Philadelphia were simply un eroded rem- 

 nants of the same general formation. As the consensus of opinion favors 

 the view that the Lafayette outliers on the Piedmont Plateau were once 

 united with the other areas of the Coastal Plain, the fourth requisite will 

 be considered as fulfilled. 



The same explanations which have been given above in regard to the 

 Lafayette plat and diagram are applicable to that of the Sunderland for- 

 mation on Plate XXIV. It may be said, however, that in this case there 

 is a scarp and, therefore, a datum line preserved. All the stations are 

 located along this scarp-line with the exception of the one at Olivet in 

 southern Maryland. This has been included so as to introduce the ele- 

 ment of slope away from the scarp-line and is located at the extreme edge 

 of the Sunderland surface. A comparison of the averages will show none 

 exceeding 3.5 feet per mile while many of them have no variations in 



