that are preserved in the Strata of the Carboniferous Order, beginning with those which are common both to the ancient and existing states of Vegetable Life.

Equisetaceæ.*

Among existing vegetables, the Equisetacea are well known in this climate in the common Horse-tail of our swamps and ditches. The extent of this family reaches from Lapland to the Torrid Zone, its species are most abundant in the temperate zone, decrease in size and number as we approach the regions of cold, and arrive at their greatest magnitude in the warm and humid regions of the Tropics, where their numbers are few.

M. Ad. Brongniartt has divided fossil Equisetaceæ into two Genera; the one exhibits the characters of living Equiseta, and is of rare occurrence in a fossil state; the other is very abundant, and presents forms that differ materially from them, and often attain a size unknown among living Equisetacea; these have been arranged under the distinct genus Calamites, they abound universally in the most ancient Coal formation, occur but sparingly in the lower strata of the Secondary series, and are entirely wanting in the Tertiary formations, and also on the actual surface of the earth.

The same increased development of size, which in recent

*See Pl. 1. Fig. 2.

+ Histoire des Végétaux Fossils, 2d Livraison,

+ Calamites are characterized by large and simple eylindrical stems, articulated at intervals, but either without sheaths, or presenting them under forms unknown among existing Equiseta; they have sometimes marks of verti cillated Branches around their articulations, the leaves also are without joints. But the most obvious feature wherein they differ from Equiseta, is their bulk and height, sometimes exceeding six or seven inches in diameter, whilst the diameter of a living Equisetum rarely exceeds half an inch. A Calamite fourteen inches in diameter has lately been placed in the Museum at Leeds.

Equisetaceae accompanies their geographical approximation to the Equator, is found in the fossil species of this order to accompany the higher degrees of Antiquity of the strata in which they occur; and this without respect to the latitude, in which these formations may be placed. M. Ad. Brongniart (Prodrome, p. 167) enumerates twelve species of Calamites and two of Equiseta in his list of plants found in strata of the carboniferous order.

Ferns.*

The family of Ferns, both in the living and fossil Flora, is the most numerous of vascular Cryptogamous plants.† Our knowledge of the geographical distribution of existing Ferns, as connected with Temperature, enables us in some degree to appreciate the information to be derived from the character of fossil Ferns, in regard to the early conditions and Climate of our globe.

The total known number of existing species of Ferns is about 1500. These admit of a threefold geographical distribution:

1. Those of the temperate and frigid zone of the northern hemisphere, containing 144 species.

2. Those of the southern temperate zone, including the Cape of Good Hope, parts of South America, and the extratropical part of New Holland, and New Zealand, 140 species.

* See Pl. I. No. 6. 7. 8. 37. 38. 39.

Ferns are distinguished from all other vegetables by the peculiar divi. sion and distribution of the veins of the leaves; and in arborescent species, by their cylindrical stems without branches, and by the regular disposition and shape of the scars left upon the stem, at the point from which the Petioles, or leaf stalks, have fallen off. Upon the former of these characters M. Ad. Brongniart has chiefly founded his classification of fossil Ferns, it being impossible to apply to them the system adopted in the arrangement of living Genera, founded on the varied disposition of the fructification, which is rarely preserved in a fossil state.

3. Those which grow within 30 or 35 degrees on each side of the Equator, 1200 species.

If we compare the amount of Ferns with the united numbers of other tribes of plants, we may form some idea of the relative importance of this family in the vegetation of the district, or period to which we apply such comparison. Thus, in the entire number of known species of plants now existing on the globe, we have 1500 Ferns and 45,000 Phanerogamiæ, being in the proportion of 1 to 30. In Europe this proportion varies from 1:35 to 1: 80, and may average 1:60. Between the Tropics, Humboldt estimates the number in Equinoxial America at 1:36, and Mr. Brown gives 1:20 as the proportion in those parts of intertropical Continents which are most favourable* to Ferns.

Mr. Brown (Appendix to Tuckey's Congo Expedition) states that the circumstances most favourable to the growth of Ferns are humidity, shade, and heat. These circumstances are most frequently combined in the highest degree in small and lofty tropical islands, where the air is charged with humidity, which it is continually depositing on the mountains, and thereby imparting freshness to the soil. Thus in Jamaica Ferns are to the Phanerogamiæ nearly in the proportion of 1 to 10; in New Zealand as 1 to 6; in Taiti as 1 to 4; in Norfolk Island as 1 to 3; in St. Helena as 1 to 2; in Tristan d'Acunha (extratropical) as 2 to 3. Ferns also are the most abundant Plants in the Islands of the Indian Archipelago.

It appears still farther, that not only are certain Genera and tribes of Ferns peculiar to certain climates, but that the enlarged size of the arborescent species depends in a great degree on Temperature, since Arberescent Ferns are now found chiefly within, or near the limit of the Tropics.†

* Botony of Congo, p. 42.

+ The few exceptions to this rule appear to be confined to the southern

From the above considerations as to the characters and distribution of living Ferns, M. Ad. Brongniart has applied himself with much ingenuity, to illustrate the varying condition and climate of our Globe, during the successive periods of geological formations. Finding that the fossil remains of Ferns decrease continually in number, as we ascend from the most ancient to the most recent strata, he founds upon this fact an important conjecture, with respect to the successive diminutions of temperature, and changes of climate, which the earth has undergone. Thus, in the great Coal formation there are about 120 known species of Ferns, forming almost one half of the entire known Flora of this formation; these species represent but a small number of the forms which occur among living Ferns, and nearly all belong to the Tribe of Polypodiaceæ, in which Tribe we find the greater number of existing arborescent species.* Fragments of the stems of arborescent Ferns occur occasionally in the same formation. M. Brongniart considers these circumstances as indicating a vegetation, analogous to that of the Islands in the equinoctial regions of the present Earth; and infers that the same conditions of Heat and Humidity which favour the existing vegetation of these islands, prevailed in still greater degree during the formation of the Carboniferous strata of the Transition Series.

hemisphere, and one species is found in New Zealand as far south as lat. 46°. See Brown in Appendix to Flinder's Voyage.

* In Plate 1, figs. 7, and 37, represent two of the graceful forms of arborescent Ferns which adorn our modern tropics, where they attain the height of forty and fifty feet.

An arborescent Fern forty-five feet high (Asophila brunoniana,) from Silhet in Bengal, may be seen in the staircase of the British Museum. The stems of these Ferns are distinguished from those of all arborescent Monocotyledonous plants, by the peculiar form and disposition of the scars, from which the Petioles or leaf stalks have fallen off. In Palms and other arborescent Monocotyledons, the leaves, or Petioles, embrace the stem and leave broad transverse scars, or rings, whose longer diameter is horizontal. In the case of Ferns alone, with the single exception VOL. I.-30

In strata of the Secondary Series, the absolute and relative numbers of species of Ferns considerably diminishes, forming scarcely one third of the known Flora of these midway periods of geological history. (See Pl. 1. Figs. 37. 38. 39.)

In the Tertiary Strata, Ferns appear to bear to other vegetables nearly the same proportion as in the temperate regions of the present Earth.

Lepidodendron.*

The genus Lepidodendron comprehends many species of fossil Plants, which are of large size, and of very frequent occurrence in the Coal formation. In some points of their structure they have been compared to Coniferæ, but in other respects and in their general appearance, with the exception of their great size, they very much resemble the Lycopodiaceae, or Club Moss Tribe. (See Pl. 1. Figs. 9. 10.) This tribe at the present day, contains no species more than three feet high, but the greater part of them are weak, or creep

of Angiopteris, the scars are either elliptic or rhomboidal, and have their longer diameter vertical.

M. Ad. Brongniart (Hist. des. Veg. Foss. p. 261, Pl. 79. 80.) has described and figured the leaf and stem of an arborescent fern (Anomopteris, Mougeottii) from the variegated sand-stone of Heilegenberg in the Vosges. Beautiful leaves of this species, with their capsules of fructification sometimes adhering to the pinnules, abound in the New red sand-stone formation of this district.

M. Cotta has published an interesting Work on fossil Remains of arborescent ferns, which occur abundantly in the New red sand-stone of Saxony near Chemnitz. (Dendrolithen. Dresden and Leipsig, 1832.) These consist chiefly of Sections of the Trunks of many extinct species, sufficiently allied in structure to that of existing arborescent Ferns, to leave little doubt that they are the remains of extinct species of arborescent Plants of this family, that grew in Europe at this period of the Secondary formation.

*Pl. 1. Figs. 11. 12. and Pl. 55, Figs. 1. 2. 3.