82 THE PLIOCENE AND PLEISTOCENE DEPOSITS OF MAEYLAND 



dominant element in the structure. Combined with it is a slight tilting 

 as the result of the various complicated movements which the Coastal 

 Plain has undergone since its deposition. There is not enough data 

 to accurately separate these two elements, but it is believed that the tilt- 

 ing is usually of less imj)ortance than the initial slope in determining the 

 present attitude of the formation. As these elements have entered into 

 the structure of all the other surficial formations, from the Sunderland to 

 the Talbot, this discussion will not be repeated in describing them. At 

 the head of the Bay the slope of 17 feet per mile has in all probability 

 a larger element of tilting than of initial slope, for the underlying 

 Potomac beds indicate in their structure that the region has been 

 relatively elevated toward the west, or depressed toward the east. The 

 age of the Potomac beds in this locality is very much greater than that 

 of the Lafayette and this deformation may have been partly imposed on 

 the region before the Lafayette was deposited or it may not. The most 

 that can be said here is that the beds slope toward the southeast at the 

 rate of 17 feet per mile. 



The thickness of the Lafayette formation is not great. On Black hill 

 near Elk Neck, Cecil county, it amounts to a little more than 100 feet. 

 In other localities the basal portions are not visible and the thickness 

 cannot be determined, while in still other places the formation thins 

 down to nothing and disappears. Taken as a whole, the average thick- 

 ness probably does not reach 50 feet. 



Character of Materials. — The materials composing the Lafayette 

 formation consist of clay, loam, sand, gravel, and iron ore which is present 

 in the deposit as a cement, binding the loose materials together in ledges 

 of local development. It does not, so far as is known, occur in quantities 

 sufficiently extensive for mining (Plate III, Fig. 2). 



These materials were imperfectly sorted by the waves of the Lafayette 

 sea, so that they are now found intermingled in varying proportions. 

 Although there is a rough bipartite division in the deposits as a whole, 

 whereby the gravel occurs in greater abundance at the base and the sand 

 and loam at the top of the formation, yet these elements are mixed 



