With the end of the Silurian period the Age of Invertebrates comes to a close, giving place to the Devonian, the Age of Fishes.
Fig. 295. Block of Limestone showing Interior Casts of Pentamerus oblongus, a Common Silurian Brachiopod
THE DEVONIAN
In America the Silurian is not separated from the Devonian by any mountain-making deformation or continental uplift. The one period passed quietly into the other. Their conformable systems are so closely related, and the change in their faunas is so gradual, that geologists are not agreed as to the precise horizon which divides them.
Subdivisions and physical geography. The Devonian is represented in New York and southward by the following five series. We add the rocks of which they are chiefly composed.
| 5 Chemung | ..... | sandstones and sandy shales |
| 4 Hamilton | ..... | shales and sandstones |
| 3 Corniferous | ..... | limestones |
| 2 Oriskany | ..... | sandstones |
| 1 Helderberg | ..... | limestones |