. Elements of geology : a text-book for colleges and for the general reader. Geology. 304: PALEOZOIC SYSTEM OF ROCKS. Plants. With the exception of a few small land-plants, ferns, and club- mosses, recently found in the Middle Silurian of both this country and Europe,* and of which we shall speak again, the only plants yet found are the lowest forms of cellular cryptogams, viz., marine algce or sea- weeds. It is difficult, from the impressions left by these to determine genera, much more species, with any degree of certainty. We shall, therefore, call them by the general somewhat indefinite na
. Elements of geology : a text-book for colleges and for the general reader. Geology. 304: PALEOZOIC SYSTEM OF ROCKS. Plants. With the exception of a few small land-plants, ferns, and club- mosses, recently found in the Middle Silurian of both this country and Europe,* and of which we shall speak again, the only plants yet found are the lowest forms of cellular cryptogams, viz., marine algce or sea- weeds. It is difficult, from the impressions left by these to determine genera, much more species, with any degree of certainty. We shall, therefore, call them by the general somewhat indefinite name of Mu- coids (Fucus, tangle or kelp), or Fucus-like plants. As already stated, plants are far less abundantly and perfectly preserved than animals, on account of their want of a skeleton. Animals. Protozoans.—The large, irregular masses which are called Eozoon seem entirely characteristic of Archaean times. If they are indeed of animal origin, they are replaced in the Silurian age by more regular forms which are usually called sponges. Of these, the most character- istic Silurian genera are Stromatopora and Eeceptaculitis (Figs. 297 - 303). They seemed to have formed large coral- line masses,which are now regarded either as hydrocorals (Stro- matopora) or as com- pound Khizopods (Receptaculitis). Radiates, Corals.—Corals were very abundant, forming often whole rock-masses, as if they, while living, formed reefs. These, if they in- dicate warm seas, show a great uniformity of temperature, since they are found in all portions of the earth alike. The corals of the Silurian age belong principally to three families, viz., Cyathophylloids, or cup-corals ; Favositidaz, or lioney-combed cor- als ; and Halysitidm or chain-corals. They are remarkable in not. Fig. 297.—Stromatopora rugosa. Lesquereux, American Journal of Science, 18*78, vol. xv, p. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - co
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