MARYLAND GEOLOGICAL SURVEY 111 



It was not considered necessary to go into many particulars, but simply 

 to convey a broad idea of the region. The time bas now arrived, how- 

 ever, to present in more detail the true character of these various terrace 

 formations. 



The older surficial formations, in order to harmonize with the Recent 

 terrace, should first possess a plain surface, gently sloping toward the 

 ocean or the surrounding estuaries. Second, this plain should be sepa- 

 rated by a scarp-line from every other and from the higher ground along 

 the margin of the Piedmont Plateau. Third, the datum line, or the line 

 where each terrace comes in contact with the scarp, should be practically 

 at a constant level if the deposit was raised parallel to its former position, 

 or should slope gradually up or down if the terrace has suffered moder- 

 ate deformation. Fourth, each terrace deposit should either be, or show 

 conclusive evidence, that it once was continuous about the borders of the 

 estuaries and along the ocean front. A comparison will now be made 

 between the older terrace formations in order to show that each possesses 

 these essential characteristics. 



In order to show that each one of the older terrace formations possesses 

 these characteristics, a series of diagrams has been prepared which are 

 shown in Plates XXIII, XXIV, XXV, and XXVI. Each diagram deals 

 with a single terrace formation and consists of a series of calculations 

 derived from ten distinct localities scattered widely over the surface of 

 the terrace. Accompanying each one of these diagrams is a map on which 

 the various stations are indicated with an asterisk and their elevations 

 above sea-level are expressed in figures. By examining the illustration 

 devoted to the Lafayette terrace (Plate XXIII) it will be seen, first, that 

 the ten stations are broadly distributed throughout the surface of the 

 Lafayette, including not only the area of greatest development south of 

 Washington, but also the more important of the outliers in the Coastal 

 Plain and along the margin of the Piedmont Plateau. These stations 

 were selected not only because they were well scattered throughout the 

 district, but also for the reason that they Avere considered as being char- 

 acteristic and representative of the various elevations of the Lafa} r ette 

 surface. It will be noticed that six of them lie on the higher elevations 



