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. [Illustration: FIG. 27.--_Fenestella retipora_. Mountain limestone.] [Illustration: FIG. 28.--_Goniatites_. Mountain limestone.] We have evidence of the existence in the forests of a variety of _centipede_, specimens having been found in the erect stump of a hollow tree, although the fossil is an extremely rare one. The same may be said of the only two species of land-snail which have been found connected with the coal forests, viz., _pupa vetusta_ and _zonites priscus_, both discovered in the cliffs of Nova Scotia. These are sufficient to demonstrate that the fauna of the period had already reached a high stage of development. In the estuaries of the day, masses of a species of freshwater mussel (_anthracosia_) were in existence, and these have left their remains in the shape of extensive beds of shells. They are familiar to the miner as _mussel-binds_, and are as noticeable a feature of this long ago period, as are the aggregations of mussels on every coast at the present day. [Illustration: FIG. 29.--_Aviculopecten papyraceus_. Coal-shale.] CHAPTER III. VARIOUS FORMS OF COAL AND CARBON.