342 BOTANICAL SUKVEY OF DISMAL SWAMP KEUION. 



footstep they took. To their sorrow, too, they found the weeds and 

 briers more firmly interwoven than they did the day before. But 

 the greatest grievance was from large cypresses, which the wind had 

 blown down and heaped upon one another. On the limbs of many of 

 them grew sharp snags, pointing every way like so many pikes, that 

 required much pains and caution to avoid. These trees, 1 being ever- 

 greens ["sic | and shooting their large tops very high, are easily overset 

 by every gust of wind, because there is no firm earth to steady their 

 roots. Thus many of them were laid prostrate, to the great encum- 

 brance of the way." 



GEOLOGY. 



II will be expedient to leave the description of the most recent 

 superficial deposits of the Dismal Swamp region to the following 

 chapter on "Soils," and to devote this section of the paper to a brief 

 description of the underlying si rata, so far as their character and 

 extent have been determined, merely enumerating the uppermost 

 deposits. The series of events which has created the surface topog- 

 raphy and the arrangement of the underlying geological formations 

 which we find in the Dismal Swamp region to-day has formed the 

 subject of numerous publications, and will be described in the text 

 of the Norfolk folio of the Geological Atlas of the United States, soon 

 to be issued by the United Slates Geological Survey. While the 

 present distribution of the vegetation of the region is undoubtedly in 

 pari a result- of its past geological mutations, the subject is too exten- 

 sive to be entered upon in this report, even were the data at hand for 

 its proper presentation. Consequently we shall confine ourselves to 

 a statement of existing conditions. 



The most recent surface formation of the Dismal Swamp region con- 

 sists, in the region designated as The Plain, of a soil usually loamy, 

 but varying from almost pure sand, with an insignificant content of 

 humus in the highest and best-drained portions, to a mixture of sand, 

 silt, mid considerable organic matter in I he lower-lying lands. In 

 the beach and dune area the surface formation consists entirely of 

 fine white sand of marine origin. In the swamps, on the other hand, 

 notably in the Great Dismal itself, occur heavy deposits of peat — 

 vegetable matter in various stages of decomposition— which in many 

 places reach a thickness of 3 meters (10 feet) and are sometimes 4^ 

 meters (15 l'w\) thick. Toward the margins of the Dismal Swamp 

 these vegetable deposits gradually decrease in thickness. Great 

 numbers of trunks of large trees have been buried in the peat, and 

 are often so well preserved as to be valuable for all purposes to which 

 newly felled timber can be put. 1 The surface of the salt marshes is 

 covered with a thin layer of brownish or gray silt, mixed with con- 

 siderable decaying organic matter and saturated with water which 

 contains usually 2 to ;5 per cent of sodium chloride. Under this a 

 layer of stiff, blue clay often occurs. 



1 See N. B. Webster, Amer. Naturalist, vol. 0. pp. 200 to 2(52 (1875). 



