OF THE UNITED STATES. 9 
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. Manteil, (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 cxide 
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 
