15 



looked upon as in the case of a very similar material recently made 

 the subject of minute inquiry by my brother in New Jersey, as a 

 remnant or outlying portion of a once somewhat extensive deposite 

 of ferruginous gravel and conglomerate, which by subsequent de- 

 nuding action has been almost entirely removed. 



The matter which in most cases rests immediately upon the 

 shells, is a yellowish brown sand, frequently 'containing a large 

 proportion of clay. Throughout this mass, and often extending to 

 the distance of five or six feet from the shells, particles of green 

 sand, or the silicate of iron and potash, are more or less abundantly 

 disseminated ; and in the immediate vicinity of the shells, these par- 

 ticles are generally condensed into narrow stripes conforming in 

 flexure to the irregularities of the bed beneath. Even where a 

 deep hole exists in the layer of shells, the stripes of green sand are 

 seen still following the depression and rise of the surface, and pre- 

 serving a uniform distance from it. Sometimes these thin layers 

 are so much indurated as to have almost the appearance of stone. 

 In none of the strata above described have fossils of any description 

 ever been discovered. 



The materials with which the shells are intermixed, or in which 

 they are embedded, have various characters. In some cases they 

 consist principally of a nearly white sand ; in others the argillaceous 

 matter greatly predominates, and the mass is a somewhat tenacious 

 clay. Frequently much oxide of iron is mingled with the earthy 

 matter, giving it more or less of a yellow or brown appearance, 

 and this is the aspect which the upper beds containing shells most 

 usually present. Very generally the lowest visible fossiliferous 

 stratum is composed of a green silicious sand, and a bluish clay, 

 which being always very moist, is soft and tenacious, and presents 

 a dark blue or black colour. At the base of the cliffs on the 

 James and York rivers, this stratum may be traced continuously 

 for considerable distances, rarely rising more than two or three feet 

 above the level of the water, and presenting an even horizontal 

 outline. In the deep ravines, and low down in the banks of shells, 

 generally, throughout this region, a similar dark bluish green argil- 

 laceous sand is observed, enclosing frequently a great number and 

 variety of shells. This constitutes what is usually denominated 

 blue marl, which from the soft condition of the shelly matter which 

 it contains, as well as the predominance of clay in its composition, 

 is found peculiarly beneficial when applied to the more arenaceous 



