Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/395

 Rh Tertiary series. Many additional species have been collected from each of these series, but are not yet named.

As the known species of living vegetables are more than fifty thousand, and the study of fossil botany is as yet but in its infancy, it is probable that a large amount of fossil species lies hid in the bowels of the earth, which the discoveries of each passing year will he continually bringing to light.

The plants of the First period are in a great measure. composed of Ferns, and gigantic Equisetaceæ; and of families, of intermediate character between existing forms of Lycopodiaceæ and Coniferæ, e. g. Lepidodendriæ, Sagillariæ, and Stigmariæ; with a few Coniferæ.

Of plants of the Second period, about one-third are Ferns; and the greatest part of the remainder are, Cycadesæ and Coniferæ, with a few Liliaceae. More species of Cycadeæ occur among the fossils of this period, than are found living on the present surface of the earth. They form more than one-third of the total known fossil Flora of the Secondary formations; whilst of our actual vegetation, Cycadeæ are not one two-thousandth part.

The vegetation of the Third period approximated closely to that of the existing surface of the globe.

Among living families of plants, Sea-weeds, Ferns, Lycopodiaceæ, Equisetaceæ, Cycadeæ and Coniferæ, bear the nearest relation to the earliest forms of vegetation that have existed upon our planet.

The family which has most universally pervaded every stage of vegetation is that of Coniferæ; increasing in the number and variety of its genera and species, at each successive change in the climate and condition of the surface of the earth. This family forms about one three-hundredth part of the total number of existing vegetables.

Another family which has pervaded all the Series of formations, though in small proportions, is that of Palms.

The view we have taken, of the connexions between the extinct and living systems of the vegetable kingdom, supplies