344 BOTANICAL SURVEY OF DISMAL SWAMP REGION. 



the subsoil of much of the region, vary considerably at different 

 points, and comprise gravel, coarse sand (sometimes quicksand), fine 

 sand, silt, and red, yellow, and blue clays, besides various mixtures 

 of sand, silt, and clay. 1 



In the greater part of the Dismal Swamp region water stands quite 

 near the surface of the soil, so that the roots of all except the smallest 

 herbaceous plants can readily penetrate to a depth at which water is 

 abundant. All deep-lying water of the region, so far as has been 

 ascertained, has a salty taste. 



SOILS. 



By Frank D. Gardner, Assistant, Division of Soils. 



THE SALT MARSHES. 



The soil of the salt marshes is usually a brown silt containing much 

 partially decomposed vegetable matter, beneath which stiff clay is 

 often present as a subsoil. Great moisture is the normal condition 

 of this soil, and at high tide it is subject to overflow. As the water 

 which then covers it is strongly brackish, the soil of salt marshes is 

 characterized by a much higher percentage of common salt (NaCl) 

 than is present in ordinary soils. 



THE SAND STRAND. 



The soil of the beach and dune area, like that of the salt marshes, 

 possesses no agricultural value. It is an almost pure marine sand, 

 whitish in color. Near the tide limit particles of carbonate of lime 

 (CaC0 3 ) are somewhat abundantly intermixed, a result of the decom- 

 position of seashells. Farther back, however, accumulation of lime 

 is prevented by the dissolving action of rain water impregnated with 

 carbonic oxide (CO.,). llumus is almost entirely wanting, except on 

 the innermost, fixed dunes. Here the growth of trees permits a suffi- 

 cient accumulation of vegetable matter to give the soil a grayish color. 

 Elsewhere the sparsencss of the vegetation, the ready permeability 

 of the sand, the mechanical effect of the wind, and the rapid oxida- 

 tion brought about by wind and sunlight are conditions which inter- 

 fere with the accumulation of dead vegetable and animal matter. 



Common salt, sodium chloride, is present in considerably larger 

 quantity near the shore than is normally the case in inland soils. The 

 presence of the salt is easily accounted for by the frequency with 

 which spray is blown landward by the wind. 



That the percentage of sodium chloride, as well as of calcium car- 

 bonate, which exists in dune sands at any considerable distance 



1 The Columbia formation is described by W. J. McGee, Am. Journ. Sci., ser. 3, 

 vol. 135, pp. 120 to 143, 328 to 330, 367 to 388, 448 to 466, 1888; and by N. H. Darton, 

 Bui. Geol. Soc. America, vol. 2, pp.431 to 400, 1891. 



