THE FOSSIL FLORA. 
197 
from a distance, and deposited here, we must conclude, that this bed 
of shells, (and there are many more known in other parts of the se¬ 
ries,) marks what had been, for some considerable period, as compa¬ 
red with the age of man, the uppermost surface of the earth, upon 
which fresh, and, probably, still water, had reposed, as in the before- 
cited case. Now, although it may be true, that the presence of or¬ 
ganic remains in any stratum, be evidence sufficient of its having 
once been at the surface, yet the additional evidence in these cases, 
is so far valuable, as it proves that these beds remained uncovered 
for a period of considerable duration ; long enough, indeed, for plants 
of a large size to flourish, and beds of muscles of considerable thick¬ 
ness to form, by the successive growth and decay of the animals. 
What an amazing idea is thus forced upon us, of the length of the 
period which might elapse, during the deposition of the Coal mea¬ 
sures alone, where the beds here referred to, are but two in hundreds, 
any one of which may have been as long uncovered by its successors 
in the series; and what is the whole of the Coal formation, compared 
with the great mass of the secondary strata ?—a single layer of stones 
in a stupendous edifice ! 
It has been already stated, that one of the seams of coal in the 
Northern Coal Field, is known over an area of 200 square miles; 
now, supposing this seam to have originated in the way generally 
believed, by a sweeping of vegetables from the land, could we, in any 
case, conceive such a mass floated down at one time, as to cover such 
a space ? And if this bed be also spread over the formation where it 
has not yet been worked, we shall have to double or treble the space ; 
if it had been so produced, is it likely it would have presented, 
throughout the whole of this extent, an absolute continuity, and an 
even thickness—this thickness being at the same time, so inconsi¬ 
derable, as rarely to exceed six feet P Should we not rather have ex- 
pected to find the vegetable matter unequally spread, and irregularly 
accumulated ? 
Again, if this seam of coal had originated in the violent action of 
a current of water, sweeping vegetables from the spots where they 
grew, would not some of the soil and detritus in which they vegeta¬ 
ted, or the loosely aggregated matter which then, at least periodically, 
existed in abundance, be washed down and mixed with them ? There 
is no evidence of violent action whatever in the beds of the coal 
measures; there is not any thing approaching a conglomerate, the 
grains of sand comprising the sandstone being the largest transported 
fragments visible. It is one remarkable character of the seams of 
rich coal, that, from the floor to the roof, (to use the miners expres- 
