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RETROSPECT OF FOSSIL BOTANY. 207 
2 
- tissues into stone, from the infiltration of siliceous, calca- 
reous, or metallic solutions, being an accidental process, 
dependent on the physical conditions under which the trees 
and plants were submerged, and entombed in the strata. 
Although the entire system of vegetable life which pre- 
vailed during the earlier ages of the world is but partially 
_ revealed by the fossil remains which geological researches 
have brought under the examination of the naturalist,—for 
numerous tribes of plants may have existed of which no 
_ traces have been detected, while of species of delicate tissues 
all vestiges may have perished,—yet a review of the facts 
hitherto obtained, presents some highly important and un- 
_ expected results, as to the characters of the successive floras 
which prevailed during the paleozoic, secondary, and ter- 
tiary epochs. And though deductions of this nature must, 
in the present state of our knowledge, be regarded in the 
light of shifting hypotheses to be modified or abandoned 
with the progress of discovery,—yet the predominating types 
which characterize the flora of one system of formations, 
differ so essentially from those of another, that it may be 
reasonably inferred such apparent distinctions are the effect 
of organic laws, and not illusions arising from our misinter- 
pretation of the natural records of former conditions of the 
vegetable world. 
The absence in the most ancient deposits of the entire 
class of Angiosperms, or flowering plants, which constitutes 
the leading features of the floras with which we are familiar, 
—the abundance of unknown types of Cryptogamia, and the 
extinction or disappearance of those tribes in the succeeding 
formations, and the prevalence of new species and genera 
belonging to another class ;—the predominance in one flora, 
both in number and variety, of certain tribes, and their de- 
cadence in the next period ; while a family subordinate in 
the antecedent epoch, and known but by a small number of 
Species, suddenly acquires a pre-eminence both in numbers 
