112 THE PLIOCENE AND PLEISTOCENE DEPOSITS OP MAKYLAND 



of the Piedmont Plateau while only four are platted in the Coastal Plain. 

 Two of these latter, at Elkton and Marriott Hill, are located on outliers. 

 Brandy wine and Charlotte Hall are placed one in the center and the 

 other at the margin of the broad Lafayette surface of southern Maryland. 

 All of the stations of the Piedmont Plateau are situated on isolated rem- 

 nants. A word may be added in regard to the various surface elevations 

 of the Lafayette along the Piedmont Plateau. The old scarp-line against 

 which the Lafayette sea must have cut has not been preserved anywhere 

 in the region under discussion. At one locality the surface elevation may 

 represent a position very close to the old scarp-line and, therefore, orig- 

 inally higher, while another one may represent a location at a considerable 

 distance from shore and, therefore, lower. This is not true of the other 

 terraces where the datum line at the base of the scarp has been preserved 

 and stations located at various points along this line can be compared 

 with a precision which it is not possible to secure in contrasting stations 

 on the Lafayette surface. Erosion has also modified these Lafayette out- 

 liers to such an extent that it is a matter of doubt whether the station is 

 located on the original surface of the Lafayette formation or at a point 

 somewhat beneath. The last remark does not apply to the stations at 

 Brandywine or Charlotte Hall for here it is reasonably certain that the 

 surface of the Lafayette has not been lowered appreciably by erosion. 



If attention is now transferred from the map to the diagram, it will 

 be seen that each one of these ten stations is accompanied by a numeral 

 showing its elevation above mean tide level, and is compared with every 

 other station. In the lower left-hand half of the diagram, the figures in 

 each square are arranged to express the following: on the first line the 

 numeral shows the difference in elevation between the two stations which 

 are compared, expressed in feet; the numeral on the next line indicates the 

 number of miles between two stations. These measurements were taken 

 on a map scaled to eight miles to the inch and are sufficiently accurate 

 for the problem at hand. No fractions are introduced ; all the distances 

 are expressed in full numbers. In the third line the numerals indicate 

 in feet the average slope of the surface per mile between the two stations. 

 These average slopes are recorded by themselves in the upper right-hand 



