MARYLAND GEOLOGICAL SURVEY 93 



Structure and Thickness. — What was said in reference to the 

 structure of the Lafayette and Sunderland is also applicable to the 

 Wicomico formation. Its basal portions are frequently obscured and it 

 was deposited on an uneven surface. A better idea of its structure can be 

 obtained from comparing its surface elevations than the elevations of its 

 basal portions. 



The surface elevations of ten localities within the Wicomico formation 

 and the average slopes between them are given on Plate XXV. From a 

 comparison of these it will be seen that between Aiken and Washington 

 there is no slope indicated. From Washington to Eidge the surface of 

 the Wicomico formation has a difference in altitude of 45 feet through- 

 out a distance of 63 miles, making an average slope of 0.7 of a foot per 

 mile. On the Eastern Shore, from Grays Hill to West, the difference in 

 altitude amounts to 55 feet in 95 miles, or an average slope of 0.5 of a 

 foot per mile. It will thus be seen that the Wicomico formation, like 

 the Lafayette and Sunderland, slopes gently toward the southeast. There 

 is only a very small element of tilting present in this structure. In 

 southern St. Mary's county, however, there is probably more than in any 

 other portion of the region. The structure then is mostly due to initial 

 slope. 



The Wicomico formation nowhere attains any considerable thickness. 

 At Turkey Point, Cecil county, it has a thickness of about 70 feet. This 

 is probably the maximum. At many other places it thins down and dis- 

 appears entirely. As a whole, its average thickness probably does not 

 exceed 25 or 30 feet. 



Character of Materials. — The materials which constitute the Wi- 

 comico formation are similar to those found in the Sunderland, and, in 

 fact, many of them have been derived from that formation. They consist 

 of clay, peat, sand, gravel, and ice-borne boulders (Plate XI, Fig. 2, and 

 Plate XVI, Fig. 2). The distribution of these materials is similar to 

 that described in the Sunderland in that they grade one into the other 

 both vertically and horizontally, with the preponderance of the coarser 

 materials at the base of the formation while the finer deposits are largely 

 developed towards the top. In the vicinity of Annapolis large quantities 

 of Eocene materials have been re-worked in the Wicomico formation, and 



