* The civic authorities of Glasgow have wisely exposed and
protected this instructive piece of Coal-forest in one of their
parks. I noticed, however that in the admirable printed
information they supply to the public, they describe the trees as
"at least several hundred thousand years old." There is no
authority in the world who would grant less than ten million
years since the Coal-forest period.
These changes are reflected in the progress of marine life,
though their influence is probably less than that of the great
carnivorous monsters which now fill the waters. The heavy
Arthrodirans languish and disappear. The "pavement-toothed"
sharks, which at first represent three-fourths of the
Elasmobranchs, dwindle in turn, and in the formidable spines
which develop on them we may see evidence of the great struggle
with the sharp-toothed sharks which are displacing them. The
Ostracoderms die out in the presence of these competitors. The
smaller fishes (generally Crossopterygii) seem to live mainly in
the inland and shore waters, and advance steadily toward the
modern types, but none of our modern bony fishes have yet
appeared.
More evident still is the effect of the new conditions upon the
Crustacea.
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