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POPULAR SCIENCE REVIEW. 
rendered defective, by the limited extent to which even those 
plants that are preserved in the rocks have been examined hy 
man. And if this is true of the carboniferous period, it is much 
more so of all the other life systems, whose only records are to 
be found in the crust of the earth, for the economic value of the 
plant products of this period have brought under observation a 
larger proportion of their remains than of those of any, we may 
almost say, of all the other geological epochs. Yet, how little 
of the 100,000 tons of coal annually brought to the surface in 
Britain, is ever scanned by the palaeontologist. It is often the 
merest accident that has led to the discovery of a new form, 
as for instance, fine and rare specimens have sometimes been 
disclosed by the splitting of the coal, when it was being con- 
sumed, and have been saved from destruction by the accidental 
glance of an educated eye. But, while the coal is brought to 
view, and a chance is given to examine its contents, the shales 
which contain the more perfect remains are left by the collier to 
form a secure roof to his mine. 
No less than 300 species of plants have been described from 
the rocks of the Coal period in Britain. Many of these are, 
however, established on imperfect materials. The specimens 
are so fragmentary that it is difficult to determine the various 
portions that belong to the same plant. The root is rarely 
connected with the stem, the stem with the branches, or the 
branches with the leaves or fruit ; consequently all these parts 
have been referred to different genera, and have received 
different names. With increased materials, and additional 
observations, the means are occasionally turning up, which enable 
us to reduce some of these genera, and while new forms are 
being described, the tendency of modern research is rather to 
decrease the number of genera and species. We shall have 
to adduce abundant evidence of this* in the course of our 
paper. 
Eliminating, as far as possible, the genera that have been 
thus erroneously founded on imperfect materials, it is remarkable 
to what a small number of forms the plants of the coal measures 
may be reduced. Ferns, and the fossils to which the generic 
names of Sigillaria , Lepidodendron, Catamites, and Dadoxylon , 
have been given, comprise almost the whole of the known Flora. 
Nearly half of the species described are ferns, but they do not 
seem to have contributed to any great extent to the formation 
of coal ; for while their vascular tissue does not easily decom- 
pose, their remains are extremely rare in coal, and they are 
chiefly known from the occurrence of their fronds in the roof 
shales. Two or three arborescent ferns have been' observed, 
but the great majority seem to have been herbaceous plants, 
which flourished on the margins of the lakes that covered the 
