Again, older than the true carboniferous age, are the Silurian anthracites of Co.  Cavan, and certain Norwegian coals, whilst in New South Wales we are confronted with an assemblage of coal-bearing strata which extend apparently from the Devonian into Mesozoic times.

Still, the age we have considered more closely has an unrivalled right to the title, coal appearing there not merely as an occasional bed, but as a marked characteristic of the formation.

The types of animal life which are found in this formation are varied, and although naturally enough they do not excel in number, there are yet sufficient varieties to show probabilities of the existence of many with which we are unfamiliar.  The highest forms yet found, show an advance as compared with those from earlier formations, and exhibit amphibian characteristics intermediate between the two great classes of fishes and reptiles.  Numerous specimens proper to the extinct order of labyrinthodontia have been arranged into at least a score of genera, these having been drawn from the coal-measures of Newcastle, Edinburgh, Kilkenny, Saaerbruck, Bavaria, Pennsylvania, and elsewhere.  The Archegosaurus, which we have figured, and the Anthracosaurus, are forms which appear to have existed in great numbers in the swamps and lakes of the age.  The fish of the period belong almost entirely to the ancient orders of the ganoids and placoids.  Of the ganoids, the great megalichthys Hibberti ranges throughout the whole of the system.  Wonderful accumulations of fish remains are found at the base of the system, in the bone-bed of the Bristol coal-field, as well as in a similar bed at Armagh.  Many fishes were armed with powerful conical teeth, but the majority, like the existing Port Jackson shark, were possessed of massive palates, suited in some cases for crushing, and in others for cutting.

[Illustration:  FIG. 24.—­Archegosaurus minor.  Coal-measures.]

[Illustration:  FIG. 25.—­Psammodus porosus.  Crushing palate of a fish.]

[Illustration:  FIG. 26.—­Orthoceras.  Mountain limestone.]

In the mountain limestone we see, of course, the predominance of marine types, encrinital remains forming the greater proportion of the mass.  There are occasional plant remains which bear evidence of having drifted for some distance from the shore.  But next to the encrinites, the corals are the most important and persistent.  Corals of most beautiful forms and capable of giving polished marble-like sections, are in abundance. Polyzoa are well represented, of which the lace-coral (fenestella) and screw-coral (archimedopora) are instances. Cephalopoda are represented by the orthoceras, sometimes five or six feet long, and goniatites, the forerunner of the familiar ammonite.  Many species of brachiopods and lammellibranchs are met with. Lingula, most persistent throughout all geological time, is abundant in the coal-shales, but not in the limestones. Aviculopecten is there abundant also.  In the mountain limestone the last of the trilobites (Phillipsia) is found.