340 On Proto-carbonate of Iron in Coal Measures. 
with the impressions and carbonized remains of plants, are at the 
same time more or less impregnated with this ferruginous com- 
pound. So, again, the soft argillaceous shales, in the midst of 
which the lenticular ore so frequently presents itself, show by 
their dark color and included impressions of plants, as well as by 
actual analysis, that they are richly imbued with vegetable mat- 
Nor do the nearly white fire-clays, which in many cases 
inclose thick courses of the lenticular ore, form any exception to 
this law. For although in their present state they contain little 
or no carbonaceous matter, the marks of innumerable roots of 
Stigmaria, and parts of other plants which every where penetrate 
the mass, show that at one tiine they must have been crowded 
with vegetable remains. : 
A further and yet more striking proof of the influence which 
the contiguous vegetable matter has had, in the formation of the 
proto-carbonate, is seen in the fact, that the most productive lay- 
ers of the ore are commonly met with quite near to the beds 0 
coal, and that frequently courses of the nodules are found in the 
earbonaceous shales or partings which lie in the midst of the 
seam itself, er 
While the strata including the proto-carbonate are thus distin- 
charged with vegetable matter, as for example the barren shales 
of the Seral coal rocks before alluded to, contain much red ma- 
terial, both in distinct strata and mottling the general mass, and 
are throughout more or less impregnated with the sesquioxyd. 
A like general law as to color would seem to apply to the other 
great groups of sedimentary rocks, which include in particular 
beds accumulations of vegetable or other organic exuvie. us, 
in the New and Old Red Sandstone formations, which generally 
include so large a proportion of sediment colored by the red oxyd 
ly 
and when present are met with almost exclusively in the gray 
and olive and dark-colored strata which are interpolated in cer- 
tain parts of the great masses of red material. This relation 18 
beautifully shown in the middle secondary rocks of the Atlantic 
slope, which extend in a prolonged belt from the Connecticut 
Valley into the State of South Carolina. In the strata of red 
sandstone and shale, which form the chief part of the mass, vege 
table or animal exuvie are almost entirely absent. But where 
the remains of fish, and impressions of carbonized parts of plants, 
