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the first of these theories, I would observe, that although a 
considerable diminution in number is evident as we proceed 
from the older to the newer strata, and still further, that 
plants of a different character almost invariably mark each 
succeeding epoch, commencing with those of a strictly- 
tropical aspect and gigantic dimensions, which gradually 
disappear and give place to those of our own time, as Elms, 
Chesnuts, Sycamores, &c. ; still I must again declare I 
cannot see that these facts afford sufficient evidence that a 
multitude of other plants were not co-existent with those 
whose remains are preserved, but rather of the perishable 
nature of the majority of them. 
Connected with this subject there is another fact of great 
importance to be considered, that of the circumstances under 
which each peculiar group of fossil plants may have been de- 
posited. The beds of coal, for instance, consist of one homo- 
geneous mass of vegetable reliquae, grown for the most part 
on the spot, and which, after accumulating for ages and 
undergoing a chemical change in fresh water, have been sub- 
mitted to enormous pressure, the probable influence of igneous 
agency and the muriatic acid of the ocean ! Here, then, 
we have a right to expect a tolerable number of different 
species of plants. But if we turn to the Lias, and other 
sections of the Oolitic series, we find only comparatively few 
plants, and those fragments, which have been transported 
with the clay, sand, or other materials, from a distance, and 
deposited singly or collectively, as the currents happened 
to be laden with vegetable debris. Neither of these instances, 
however, furnishes satisfactory data from whence we can pre- 
dict as to the richness or sterility of vegetation at particular 
epochs ; inasmuch as the former gives us only such plants as 
flourished in the localities where our coal fields originated, and 
the latter only a few of such species as grew in the districts 
through which the inundating current might sweep. But as 
