Orthis orbicularis, J. Sow. Delbury. Upper Ludlow.
Fig. 410.
Terebratula navicula, J. Sow. Aymestry limestone; also in Upper and Lower Ludlow.
Among the fossil shells are species of Leptæna, Orthis, Terebratula, Avicula, Trochus, Orthoceras, Bellerophon, and others.[352-A]
Some of the Upper Ludlow sandstones are ripple-marked, thus affording evidence of gradual deposition; and the same may be said of the accompanying fine argillaceous shales which are of great thickness, and have been provincially named "mudstones." In these shales many zoophytes are found enveloped in an erect position, having evidently become fossil on the spots where they grew at the bottom of the sea. The facility with which these rocks, when exposed to the weather, are resolved into mud, proves that, notwithstanding their antiquity, they are nearly in the state in which they were first thrown down.
The scales, spines (ichthyodorulites), jaws, and teeth of fish of the genera Onchus, Plectrodus, and others of the same family, have been met with in the Upper Ludlow rocks.
Fig. 411.