Middle Atlantic Coastal Plain. 505 



of the Sunderland terrace. Where the streams have eroded 

 the Sunderland, as well as at many points along the landward 

 extension of the Brandywine formation where the interval 

 between the terrace levels increases, the underlying formations 

 appear in outcrop beneath the Brandywine. 



Local Brandywine area. — Brandywine, Prince George's 

 County, Maryland, is located on the slightly-eroded surface of 

 the old Brandywine terrace not far from the center of the 

 largest tract still preserved intact. The surface materials in 

 this region consist of sandy loams, while the deeper trenches 

 cut by the streams around the margin of the tract show irregu- 

 lar heds of coarse sand and gravel, the latter generally small in 

 size. The formation attains its maximum thickness in the 

 general area in which Brandywine is situated. No section of 

 the formation is exposed at Brandywine since it is situated on 

 the uneroded surface of the formation, but the adjacent ravines 

 both to the east and west cut through the formation, exhibit- 

 ing the gravels, sands, and loams characteristic of the for- 

 mation. 



Interpretation of history.— The Brandywine epoch was 

 opened by a depression of the continent border which carried 

 the waters of Brandywine time over the eroded Tertiary and 

 Cretaceous deposits to well within the Piedmont area. A 

 small outlier of questionable origin but containing gravels 

 similar to those of the Brandywine formation is found far 

 within the Piedmont in the Frederick valley, at an elevation 

 which corresponds with the possible transgression of the sea 

 into the broader valleys of the Piedmont district. At all 

 events, the tilting of the coastal area must have brought about 

 renewed erosion of the adjacent land with the result that 

 extensive and more or less heterogeneous accumulations of 

 gravels, sands, and clays were deposited rapidly along the 

 margin of the Brandywine sea, or more widely scattered with- 

 out much sorting by the currents and undertow of the period. 

 Many of the deposits, especially the coarser types, point to a 

 fluviatile origin of the materials, and many of the beds show in 

 their irregular and confused stratigraphy, characters such as oc- 

 cur from a combination of fluviatile and flood-plain deposition. 

 At the same time commingled with these probable fluviatile 

 elements are other materials of distinctly marine or estuarine 

 origin, and it, therefore, seems probable that a combination of 

 fluviatile and off-shore agencies must be predicted for the 

 formation of the Brandywine deposits. Furthermore, the 

 broad terrace plain, formed of materials of no great thickness, 

 which gradually thicken seaward as so often occurs in near- 

 shore marine beds, point to the existence of a large body of 

 water into which the ill-sorted materials of the time were 



