OF THE UNITED STATES. \) 



Again, these earths are of a yellowish brown color, fria- 

 ble or compact, and filled with green specks of silicate of 

 iron. Some of the greenish varieties are extremely indu- 

 rated, rendering it difficult to separate the contained fos- 

 sils. The friable blue marls sometimes embrace a large 

 proportion of mica in minute scales, similar to the beds 

 described by Mr. Mantel], (South Downs, p. 77,) as oc- 

 curring in the green sand of Sussex, England. 



Other localities present beds of siliceous gravel, (tur- 

 tia? of the French,) the pebbles varying in size from 

 coarse sand to an inch in diameter : these are either in- 

 sulated or cemented by green phosphate and brown oxide 

 of iron, and contain a profusion of fossils. 



At the Chesapeake and Delaware canal, I observed a 

 fine siliceous sand of a green color, answering to the 

 glauconie sableuse of Brongniart: also, a white sand 

 with abundance of lignite, which, however, appears to 

 be much more recent than the cretaceous formations. 



The friable blue marls seldom contain more than five 

 per cent, of lime, and often no trace of it, as in the ana- 

 lysis of Mr. Seybert; but Mr. Vanuxem remarks that 

 the proportion of this earth increases in the southern 

 states. 



The diversified appearances above mentioned, pass by 

 insensible degrees into each other, producing an almost 

 endless variety of mineralogical characters. 



The mineral substances found in these marls, are iron 

 pyrites in profusion ; succinite, lignite, and spheroidal 

 masses of a dark green color, and compact, sandy struc- 

 ture, probably analogous to those found in the green sand 



B 



