Middle Atlantic Coasted Plain. 503 



They are more largely found at the top than lower in the for- 

 mation but may occur at all levels. They are frequently inter- 

 mingled with the sands and gravels, forming sandy and gravelly 

 loams, often making a matrix for cobbles of considerable size. 

 The loam capping of the formation, which occurs widely, 

 varies from a few inches to 10 feet or more in thickness. In 

 the landward portions of the formation the loam contains con- 

 siderable iron and at times has a decided orange color. In 

 some areas, particularly in northern Charles County, it has a 

 pronounced mottling of drab and brick-red which is particu- 

 larly noticeable when the material is wet. The loams in the 

 seaward portions of the formation are generally grayish-yellow 

 in color. Although often mixed with gravel and sand the 

 loams are in places very argillaceous and fine in texture, espe- 

 cially in the upper portions of the formation. They have at 

 times irregular beds of coarse sands or even gravel interstrati- 

 fied with them, thin seams of gravel not being an uncommon 

 feature. The loams are frequently very hard and compact, 

 especially when rich in hydroxide of iron. Both the sands 

 and the loams, particularly the gravelly or sandy loams, show 

 a marked case-hardening on exposure to the weather. 



The Brandywine formation has a thickness of from 10 to 30 

 feet, the thickness for the most part increasing from the land- 

 ward toward the seaward margin of the formation, although 

 there are many exceptions to this rule where the deposits have 

 been laid down in the inequalities of the surface of pre-Brandy- 

 wine time. Exceptional thicknesses of over 50 feet have been 

 found. In general the coarser materials toward the landward 

 margin have a thickness of from 5 to 15 feet while in the sea- 

 ward portion of the formation the finer sands and loams reach 

 from 20 to 30 feet. 



~No determinable fossils have been recognized in the type 

 area although Darton refers to the presence of a few indeter- 

 minable molluscan shells in Virginia which may well be 

 reworked Miocene forms. 



The soils most widely distributed on the Brandywine forma- 

 tion have been described by the United States Bureau of Soils 

 as the Leonardtown loam, the Windsor sand, and the Norfolk 

 sand. The Leonardtown loam is generally found where the 

 upper layers of the Brandywine formation are loamy and con- 

 sist of a yellow silty loam having an average depth of about 

 10 inches. It is underlain by a heavier yellow loam which 

 usually grades into a mottled loam at a depth of from 28 to 32 

 inches. More or less sand and gravel generally appear in the 

 subsoil. Along the borders of this soil type the sand and 

 gravel become more prominent as the soil becomes thinner and 

 the Leonardtown loam grades over into more stony and 



