Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/353

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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 Flinders's Voyage.