4:90 
probable illustration of the processes by which the formation of a 
coal-field has been conducted. We may assume the areas now co- 
vered with coal to have been extensive flats and estuaries, receiving 
at intervals, during seasons of flood, large deposits of silt and sand, 
interspersed with leaves and broken branches and trunks of trees, 
drifted down with the detritus of not far distant lands. We may 
conceive large portions of the surface of these sedimentary deposits, 
after the cessation of the floods by which they were respectively 
transported, to have become the site of broad and shallow ponds 
or lagoons, which were speedily filled with a matted mass of floating 
stems and leaves of Stigmaria, to the exclusion of all other plants, 
‘in the same manner as the social plant, Stratiotes aloides, now crowds 
the ditches and shallow ponds in Holland, until the water is filled 
with a dense assemblage of individuals of this single species, leaving 
no intervals for the growth of any other plants. We may further 
admit, that by the deposition of mud or silt between the stems and 
leaves of Stigmaria, the bottom of each lagoon might have been 
overspread with the earthy sediments that compose the beds of fire- 
clay immediately below the coal; and that the same lagoon, after 
the deposition of these sediments, continued crowded with Stigmarie, 
accumulating on one another until they had entirely filled the lagoon 
with a matted mass of stems and leaves, as modern shallow lakes 
are gradually filled up and converted into peat-bogs. The surface 
of the lagoon thus changed to a morass may forthwith have become 
covered with a luxuriant growth of marsh plants, e. g. with Calamites, 
Lepidodendra, Sigillariz, &c., the exuvize of which formed a super- 
stratum of vegetable matter convertible to coal, resting upon a sub- 
_ stratum composed exclusively of remains of Stigmarize. The re- 
gions which were the site of this vegetable growth may, by success- 
ive subsidences, have been so reduced below the level of the water, 
as to make them the receptacles of alternating deposits of sand and 
clay (now converted to strata of sandstone and shale) between the 
several beds of incipient coal. During these processes, successive 
series of lagoons may have covered large portions of each last- 
formed drift; and every lagoon becoming the site of a renewed 
growth of Stigmariz, may thus continuously have been laying the 
foundation and nourishing the materials of future beds of inestima- 
bly precious fuel. 
In the case of beds of coal that alternate with marine deposits, it 
has been suggested that extensive subsidence of the estuaries on 
which lacustrine and terrestrial plants were growing, may have re- 
duced these estuaries below the level of the sea, where the sub- 
merged strata of vegetable matter became covered with beds of en- 
crinal limestone and other marine sediments; and that as these re- - 
ceived upon their surface further sediments of sand and mud 
drifted by land-floods into the salt-water, the estuaries were gradu- 
ally filled up, and again converted into lagoons, upon which a re- 
newed growth of lacustrine and land plants forthwith began to ac- 
cumulate the materials of other beds of coal. 
Both in the marine and the freshwater strata that alternate with 
