Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 398 CORAL-KAG. [Ch. XX. m an upward direction, there is no similar discordance as we proceed downwards, and pass from one to another of the several members of the Jurassic group, the Upper, Middle, and Lower Oolite, and the Lias. Thus, for example, I find on consulting Mr. Etheridge's tables of British Fossils,* that of sixty species of all classes that lived in the period of the Kimmeridge clay, twenty, or about 33
Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 398 CORAL-KAG. [Ch. XX. m an upward direction, there is no similar discordance as we proceed downwards, and pass from one to another of the several members of the Jurassic group, the Upper, Middle, and Lower Oolite, and the Lias. Thus, for example, I find on consulting Mr. Etheridge's tables of British Fossils,* that of sixty species of all classes that lived in the period of the Kimmeridge clay, twenty, or about 33 per cent., pass down into the Coral-Rag; or, if we confine our attention exclusively to the mollusca, of thirty-three species in the Kimmeridge clay, eight, or 24 per cent., are common to the Coral-Rag. MIDDLE OOLITE. Coral-Rag.—One of the limestones of the Middle Oolite has been called the 'Coral-Rag,' because it consists, in part, of continuous beds of petrified corals, for the most part retaining the position in which they grew at the bottom of the sea. In their forms they more frequently resemble the reef-building -poliparia of the Pacific than do the corals of any other member of the Oolite. They belong chiefly to the genera Thecosmilia (fig. 391), Protosseis, and Tham- nasfrcea, and sometimes form masses of coral 15 feet thick. In the annexed figure of a Thamnastrcea (fig. 392), from this formation, it Fig. 391. ; Fig. 392.
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