afforded by the extinct family of Trilobites, (see Plates 45 and 46) to the history of which we shall devote peculiar consideration under the head of Organic Remains. Although nearly fifty species of these Trilobites occur in strata of the transition period, they appear to have become extinct before the commencement of the secondary series.
The Radiated Animals are among the most frequent organic remains in the transition strata; they present numerous forms of great beauty, from which I shall select the family of Crinoidea, or lily-shaped animals allied to Star-fish, for peculiar consideration in a future chapter. (See Pl. 47, Figs. 5, 6, 7.) Fossil, corallines also abound among the radiata of this period, and show that this family had entered thus early upon the important geological functions of adding their calcareous habitations to the solid materials of the strata of the globe. Their history will also be considered in another chapter.
Remains of Vegetables in the Transition Series.
Some idea may be formed of the vegetation which prevailed during the deposition of the upper strata of the transition series, from the figures represented in our first plate (Fig. 1 to 13.) In the interior regions of this series plants are few in number, and principally marine;[1] but in its superior regions the remains of land plants are accumulated in prodigious quantities, and preserved in a state which gives them a high and two-fold importance; first, as illustrating the history of the earliest vegetation that appeared upon our planet, and the state of climate and geological changes which then prevailed;[2] secondly, as affecting, in no small degree, the actual condition of the human race.
- ↑ M. A. Brongniart mentions the occurrence of four species of fucoids in the transition strata of Sweden and Quebec; and Dr. Harlan has described another species found in the Alleghany Mountains.
- ↑ The nature of these vegetables, and their relations to existing species, will be considered in a future chapter.
