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I, Lesquereux on the Coal Formations of North America. 33 
stone, and limestone. The coal and the lignite of the Pliocene 
epoch have been formed in the same way. Their shales contain 
remains of land plants, and sometimes also they are alternately 
covered by sandstone and limestone. The drift which is ex- 
tended over the whole is as evident a marine formation as the 
limestone itself, and now it is in some places more than seven 
hundred feet above the level of the ocean. Is not this succession 
of land, freshwater and marine formations, in perfect accordance 
with the alternations of the strata-of the coal measures, and can 
it be explained in any other manner than by the oscillation, 
the upheaval and subsidence of the land which supports these 
formations 
Even if the theory of continual subsidence could find in re- ° 
cent phenomena anything favorable to its support, it would be 
impossible to understand how a long protracted downward move- 
~ ment, especially of a Delta, would effect the repeated formation — 
of coal beds; how the land being completely covered by the sea 
for the formation of the limestone, could be dried up again, so 
_ that the formation of the peat could begin anew, upon its whole 
surface. The river, says the theory, was still filling up again 
the whole space, while the madrepores were’ building the lime- 
stone. But this is pure speculation which is equally contrary to 
reason and to geological facts. For, if it is true that from causes 
which have not yet been clearly explained, tne delta of the Mis- 
sissippi is slowly subsiding, it is probable that if the subsidence 
was once active enough to permit the invasion of the sea over 
its whole surface, the soft matter, sand, mud and peat, of which 
it is composed, would be washed away by the marine currents, 
the tides, the waves, &c. 
In the Report of the Geological Survey of Kentucky, I ex- 
_ pressed an opinion which does not now perfectly satisfy my 
mind. I supposed that after the formation of extensive peat 
bogs, the subsidence of the land being at first very slow, the 
first result of the downward movement was a general inundation 
either of marine or of freshwater or of both mixed together. A 
depression of only a few feet of the great swamps of Southern 
Virginia would bring — them by-and-by the waters of the 
surrounding rivers and also some water from the sea, either per- 
colating through the sand or finding its way by some friths be- 
tween the hills of sand extended along the shores. This suppo- 
sition fully explains the formation of shales covered in some 
places with marine shells and remains of fishes mixed with land 
plants of the peat bogs. For, these plants, especially the ferns, 
mostly growing upon the thick and high rootstocks could still 
live in the swamps invaded by marine water. It explains also 
the local formation of the limestone in some depression of the 
marshes or marine lakes, But I supposed that after this period 
SECOND SERIES, Vor. XXVIII, No, $2 —JULY, 1859. 
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