32 L. Lesquereux on the Coal Formations of North America. 
preserved the casts of marine shells, though not the remains. 
have found them in many places, especially near Athens, Ohio, 
where a bank of soft sandstone is full of large Producti and Tere- 
bratule. But here, as in the sandstone of the lower measures, 
the animal remains have disappeared, and the mould only is aos 
served. It is the same with the prints of fossil wood foun 
the sandstone, which only shows the casts of Tepidodendra, 
Calamites , Sigillari riz, &c.; with only a thin lamina of car 
ized bark, the whole substance of the wood having diaappesred, 
except where silicification has taken place. This show 
the fossil remains are so rare in the ge st since even a nore 
can scarcely be made on loose oe 
In the shales of some beds o 1, especially in oat south- 
western part of our coal-fields, ae remains of marine shells 
abound: some of the ies are supposed to have lived in : ink 
ish water; but most of them like the fishes found in connection 
with them, appear to be true marine species. And what at first 
may look like = Semen ae h will be explained hereafter, 
th ine times more or less mixed with 
leaves of ferns oF Paid sees and scarcely if ever with true 
marine plants or Ravel. Thus us, also, from paleontological 
evidence, the shales cannot be considered as deposits of a river 
any more than the sandstone. 
The fact that the limestone of the coal measures cannot be 
thus disposed of, is fatal to this new theory. Its marine origin 
is evident and must be accounted for. And as the ocean cannot 
be swollen, like a river, it is necessasy to admit of a subsidence 
of the land for its submersion in the sea. But the supposition of 
a continual subsidence of a vast country is truly as violent an 
hypothesis as the supposition of an alternation of upheavals and 
subsidences of the same country, and the difficulty to account 
for the first proposition is far greater. Geological forces are not 
acting forever in the same way. It is now generally acknowl- 
that mountains have not been upraised in a single move- 
ment, but by a succession of gradual efforts, or by epochs of 
upheaval succeeded by epochs of rest, and eprint of sub- 
sidence; since a diminution in the activity of the internal forces 
cannot but cause a depression by the natural resistance or the 
mass 
oma - level at the present time; the movements of t 
. bout the temple of Serapis, so clearly explained by 
fall; the appearance and disappearance of some islands, &c., 
sially in the stratification of our recent formations. The 
ports the Miocene epoch was also formed by pre bogs upon an 
upraised land. shales contain leaves of different species of 
trees of ° which the congeners are found in tropical regions. These 
shales are covered by successive strata of conglomerate, 
