"The leaf or frond of this fern is very large, tripinnate or quadripinnate; the stipes is broad and undulated; the leaflets are sessile, linear-lanceolate; the ribs pinnate, the secondary ribs perpendicular to the main rib; the first leaflet on the superior side of the pinnule adheres by its side to the rachis."--_Artis._ This fern, which closely resembles some recent species, (_Pteris aurita_,) occurs in great abundance in the shale at Alverthorpe near Wakefield. Notwithstanding the profusion with which the foliage of many kinds of ferns is distributed throughout the coal formation, the undoubted stems of tree-ferns are so rare, that it may admit of question whether some of the leaves which from the analogy of their structure to recent forms have been referred to the ferns, may not have belonged to the stems of unknown trees with which they are associated in the strata; for as, in the animal kingdom, distinct types of living organisms are often found blended in the extinct races, so in the vegetable, it is possible, that foliage and stems, of apparently discordant types, may have belonged to the same extinct species or genus of trees. This problem can only be solved by diligent and continued research in the richest localities of coal-plants. M. Brongniart remarks that every bed of coal is the product of a special vegetation, often different from that which preceded, and that which followed it. Each bed thus resulting from a distinct vegetation, is characterized by the predominance of certain impressions of plants, and the experienced miners distinguish in many cases the beds they are working, by their practical knowledge of the plants that prevail. The same beds of coal, and the deposits which cover it, ought therefore to contain the different parts of the plants that were living at the period of its formation; and by carefully studying the association of these different fossils, forming thus little special floras, generally of but few species, we may hope to acquire data by which we may advance the means of reconstructing the anomalous vegetable forms of the ancient world. M. Brongniart strongly urges attention to this circumstance in the examination of the coal strata, with the view of determining the identity of the scattered leaves, stems, and fruits, in any particular stratum. By such a procedure, much addition would be made to our knowledge of the entire structures of many of the fossil plants of which we now only know the fragments. Thus we may hope to ascertain the foliage of the Sigillariæ, the roots of which, by a similar method, have but recently been determined to be the fossils called _Stigmariæ_. [Illustration: Plate XXXIII.] PLATE XXXIII. "Carpolithe, or Fossil Seed-vessel." (_Carpolithus marginatus_, of Artis.)