MARYLAND GEOLOGICAL SURVEY 113 



half of the diagram, in order to be examined more easily, and in the 

 lower left-hand corner is placed the average slope of the formation cal- 

 culated from all the observations given in the diagram. This same 

 method of treatment has been followed in each one of the succeeding 

 diagrams. 



From a study of this diagram it is seen, first, that the Lafayette forma- 

 tion was evidently developed as a plain surface, gently sloping toward 

 the surrounding waters. In order to bring out this point more clearly, 

 it is only necessary to examine the average slopes when it will be ob- 

 served that none of them exceed 17 feet per mile, one of them sinks to 

 zero and the majority fall between 1 and 8 feet. The 17-foot slope is 

 located at the head of the Bay between Woocllawn and Elk Keck. In this 

 region two factors combine to increase the average slope. The first is 

 that with one exception this is the shortest distance between two stations. 

 Therefore, any difference in elevation will not be reduced to a low aver- 

 age by being divided by a large number of miles. The second factor is 

 that in this region the older formations of the Potomac group also indi- 

 cate more than the average tilting toward the southeast. While the age 

 of this disturbance is not known, it is probable that the Lafayette has 

 shared in the deformation. In contrast to this augmented slope, it will 

 be interesting to compare the elevations of Stockton and Washington 

 along the border of the Piedmont Plateau. Although 52 miles apart, 

 these surfaces show no variation whatever, but the three stations between 

 them are slightly higher. In order to bring out more clearly the plain 

 character of the Lafayette surface, the average slopes have been added 

 together and then divided by 45, their total number. From this it is 

 found that the average slope of the Lafayette surface between all of the 

 ten selected stations amounts to only 3.7 feet per mile. It requires only 

 a glance at the map to show that the prevailing slope of this plain is 

 toward Chesapeake Bay and the Atlantic ocean. It will be seen that all 

 of the stations located on the Coastal Plain are below those located along 

 the border of the Piedmont Plateau. The greatest slope of the plain 

 from the Piedmont to the Coastal Plain is 17 feet per mile, as indicated 

 above, at the head of the Bay. In the Potomac valley between Washing- 



