a. 〈地〉志留纪的

[ noun ]
from 425 million to 405 million years ago; first air-breathing animals
<noun.time>

Silurian \Si*lu"ri*an\, n.
The Silurian age.


Silurian \Si*lu"ri*an\, a. [From L. Silures, a people who
anciently inhabited a part of England and Wales.] (Geol.)
Of or pertaining to the country of the ancient Silures; -- a
term applied to the earliest of the Paleozoic eras, and also
to the strata of the era, because most plainly developed in
that country.

Note: The Silurian formation, so named by Murchison, is
divided into the Upper Silurian and Lower Silurian. The
lower part of the Lower Silurian, with some underlying
beds, is now separated under the name Cambrian, first
given by Sedwick. Recently the term Ordovician has been
proposed for the Lower Silurian, leawing the original
word to apply only to the Upper Silurian.