2.--Carpolithes Bucklandii. _Coralline Oolite, Malton._ 3.--Trigonocarpum olivæforme. _Snibstone Colliery._ 4.--Trigonocarpum Nöggerathi. ] The reader will observe that the fossil vegetables hitherto described belong, with but few exceptions, to the Carboniferous flora; and that the remains of Ferns, Calamites, Sigillariæ, and Lepidodendra, compose in a great measure those prodigious accumulations of mineral fuel, or coal, which supply the luxuries and necessities created by civilization. Our review of fossil plants will now assume somewhat of a botanical arrangement, and we proceed to notice some of the most characteristic vegetable forms of the secondary and tertiary formations. We commence our examination with those remarkable tribes of gymnosperms, the Cycadaceæ, which comprise the Zamiæ and Cycadeæ. Fossil Cycadaceæ. The plants of this subdivision of the vegetable kingdom, from their singular structure and mode of growth, their simple cylindrical stems, and coronets of pinnated foliage, resembling that of certain palms, their usually gyrate vernation like that of the ferns, and their anomalous inflorescence and fructification, are objects of great interest to the scientific botanist; while the abundance of their fossil remains in the secondary formations renders them of the highest importance to the geologist. [Illustration: Lign. 45. Foliage and upper part of the Stem of Cycas revoluta 1/12 _nat._ _In Kew Conservatory._] As many kinds of Zamia[120] and Cycas are cultivated in our hot-houses, the general appearance of the plants of this order must be familiar to the reader: the annexed figure of a beautiful living Cycas in the Royal Gardens at Kew, will serve to illustrate the general aspect of these exotics. [120] The Linnæan genus Zamia is now separated into five or six genera, as Encephalartos, Macrozamia, Dion, &c. The Zamiæ are short plants, with stout cylindrical stems, beset with thick scales, which are the bases of the petioles that have been shed: towards the summit the stem is garnished with a crown of elegant leaves; the fruit resembles the cones of pines. The leaves are pinnated, and very tough; their venation is either parallel as in endogens, or dichotomous as in ferns, but never reticulated as in exogens: in a young state they are coiled up like a crosier, as in ferns. The Cycadeæ have the general aspect of the Zamiæ, but differ in their fructification and other characters; and some species have the stem bifurcated towards the top, and attain a height of upwards of twenty feet; for example, _C. circinalis_. The stem in its internal structure[121] bears a close analogy to that of the Coniferæ; it has a central medullary column surrounded by a ligneous cylinder, divided by cellular medullary rays, each composed of bundles of vessels, and a thick cellular cortical investment or false-bark,[122] composed of the persistent scales that formed the bases of the petioles. (See _Pl. V. fig. 5._)