Page:A Treatise on Geology, volume 1.djvu/89

 CH. V.

The first period ends with the carboniferous system; the second includes the saliferous and magnesian systems; the third comprises the oolitic and chalk systems; the fourth is the tertiary period.

The numbers of species are now considerably augmented since the table was drawn up (1829), but the proportions are not materially affected. It is still true, that vascular cryptogamia abound in an extraordinary degree among the earlier rocks, where ferns, calamities, and what seem like gigantic lycopodiaceæ are very prevalent; that in the second and third periods cycadiform and coniferous plants (phanerogamia gymnospermia) become remarkable and frequent, though ferns and lycopodiaceæ still prevail; while it is principally in the fourth period that the usual forms of dicotyledonous plants, now so plentiful on the earth, appear at all common. Moreover, on a close examination, it appears that nearly every fossil plant is of an extinct species, and that the several periods distinguished by M. Brongniart had each its own peculiar vegetable creation, distinct from every other that preceded and succeeded it.

Zoophyta being in the present system of nature all aquatic, and mostly marine, they may be expected to occur abundantly in the marine strata of the earth. They are, indeed, very plentiful, and it is interesting to observe that all, or nearly all, the species are marine. It