Report on the projected Survey of the State of Maryland. 3 



utility for agricultural purposes — according to the species of shells 

 which it encloses, the degree of decomposition of these shells, and 

 the nature of the cement by which they are held together — being in 

 some instances greater than, in most equal to that of the mineral spe- 

 cies, described in systematic works as offering two varieties ; name- 

 ly, indurated or stone marl and earthy marl. 



These beds of shell marl occur at variable depths. They are 

 sometimes covered by a thick stratum of gravel or sand, measuring 

 from ten to thirty feet and upvvards in thickness. At other times 

 they reach nearly to the surface of the soil, and their limits, under 

 this latter circumstance, are marked by a line distinctly undulating; 

 whilst elsewhere the line of separation from the superincumbent soil 

 is horizontal, and in some localities slightly inclined. In some pla- 

 ces, the fossils in the marl bed, are its principal constituent ; that is 

 to say, consisting of numerous genera and species of shells, they are 

 bound together by a cement of their own nature, which offers an ad- 

 mixture of foreign ingredients, either argillaceous or siliceous, not 

 exceeding a ratio of fifteen or twenty per cent. Such beds are char- 

 acterized by the great predominance of that species of shells known 

 in popular language as clam shells. Other beds consist principally 

 o( scallop shells. Some contain both scallop and oyster shells; oth- 

 ers oyster shells alone. Some beds are composed principally of 

 these shells thickly imbedded in clay ; while in others, the shells, 

 and more especially the scallop shells,'-' are firmly agglutinated by an 

 argillaceous and ferruginous cement. A portion of these beds of 

 shell marl offers an inexhaustible supply of the best material that can 

 be used for improving the soil, in an extensive circle around the spots 

 on which they are deposited. 



Notwithstanding the great diversity of soils, (according to locali- 

 ties,) which is observable on the Eastern shore of Maryland, it would 

 be easy to shew, that, excluding the vegetable and animal matter, 

 contained in them, they may all be arranged under two classes; 

 namely, those containing a predominance of silicious ingredients, and 

 such as contain a predominance of argillaceous ingredients; in other 

 words, sandy soils, and clayey soils. It is presumed that the great 

 characteristic of the soil, in this portion of the territory of Maryland, 

 is an absence, or deficiency of calcareous ingredients. 



• This introductory account being mainly popular, the scientific n«n>e0 of the 

 jhells are, for the present, omitted. 



