The scene seemed to belong to the ancient world of the carboniferous period, when the forms of plants were few, and of the fern kind; when there was neither bud nor blossom, nothing but a monotonous extent of leafage, amid which no bird sang.
Thomas Hardy -- The Return of the Native
He jumped to the conclusion that this must be a forest of the Carboniferous Period.
Robert A. Heinlein -- Tunnel In the Sky
They have the mystery of ferns that disappeared a million years ago into the coal of the carboniferous era.