MARYLAND GEOLOGICAL SURVEY 117 



no doubt that the formation is continuous as it is the least broken of any 

 of the terraces. The elevations about the datum-line show that it has 

 suffered no deformation except at the southern extremity of the St. 

 Mary's peninsula where it has apparently been slightly tilted toward the 

 southeast. 



If now these various terraces are compared among themselves, it will 

 be found that the criteria of the " sequence in topographic position " can 

 be applied to discriminate the one from the other, for they lie above each 

 other like a flight of stairs. If then the sequence is established in one 

 locality, the various terraces may be discriminated in other places, first, 

 by means of " continuity in deposits/' second, by " similarity of topo- 

 graphic form," and third, by " sequence in topographic position." This 

 last method of discrimination must, however, be used with caution for it 

 has been shown that the tilting of some of the older surfaces has actually 

 brought them in places to a lower altitude than certain portions of the 

 younger terraces. For instance, at Charlotte Hall the surface of the 

 Lafayette terrace lies at 200 feet while at Marriott Hill the surface of 

 the Sunderland lies at 220 feet. It will, therefore, be seen that the topo- 

 graphic method does not imply " absolute agreement in elevation " in 

 order to discriminate between the formations, but it does imply that in 

 any one region these formations lie one above the other in successive ter- 

 races and that they slope gently from one elevation to another wherever 

 a difference occurs. 



A comparison of the averages between these various formations will 

 show that the Lafayette surface exhibits a greater average slope than 

 any of the others and that each one in turn displays successively less and 

 less average slope down to the Talbot where it becomes almost unappre- 

 ciable. This is, as pointed out above, exactly what would be expected for 

 it has been shown that the surfaces have undergone repeated deforma- 

 tions since they were deposited. The Lafayette, being oldest, was sub- 

 jected to them all while the Sunderland, Wicomico, and Talbot have suf- 

 fered successively less. 



In applying this topographic method of discrimination, it necessitates 

 examining the region carefully from end to end in order to detect defor- 



