In addition
to these, however, we meet for the first time, in deposits of
this age, with the remains of genuine land-plants, though our
knowledge of these is still too scanty to enable us to construct
any detailed picture of the terrestrial vegetation of the period.
Some of these remains indicate the existence of the remarkable genus
_Lepidodendron_--a genus which played a part of great importance
in the forests of the Devonian and Carboniferous periods, and
which may be regarded as a gigantic and extinct type of the
Club-mosses (_Lycopodiaceoe_). Near the summit of the Ludlow
formation in Britain there have also been found beds charged
with numerous small globular bodies, which Dr Hooker has shown
to be the seed-vessels or "sporangia" of Club-mosses. Principal
Dawson further states that he has seen in the same formation
fragments of wood with the structure of the singular Devonian
Conifer known as _Prototaxites_. Lastly, the same distinguished
observer has described from the Upper Silurian of North America
the remains of the singular land-plants belonging to the genus
_Psilophyton_, which will be referred to at greater length hereafter.
The marine life of the Upper Silurian is in the main constituted
by types of animals similar to those characterising the Lower
Silurian, though for the most part belonging to different species.
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