Fig. 281.
Apiocrinites rotundus, or Pear Encrinite; Miller. Fossil at Bradford, Wilts.
- a. Stem of Apiocrinites, and one of the articulations, natural size.
- b. Section at Bradford of great oolite and overlying clay, containing the fossil encrinites. See text.
- c. Three perfect individuals of Apiocrinites, represented as they grew on the surface of the Great Oolite.
- d. Body of the Apiocrinites rotundus.
Different species of Crinoideans, or stone-lilies, are also common in the same rocks with corals; and, like them, must have enjoyed a firm bottom, where their root, or base of attachment, remained undisturbed for years (c, [fig. 281.]). Such fossils, therefore, are almost confined to the limestones; but an exception occurs at Bradford, near Bath, where they are enveloped in clay. In this case, however, it appears that the solid upper surface of the "Great Oolite" had supported, for a time, a thick submarine forest of these beautiful zoophytes, until the clear and still water was invaded by a current charged with mud, which threw down the stone-lilies, and broke most of their stems short off near the point of attachment. The stumps still remain in their original position; but the numerous articulations once composing the stem, arms, and body of the zoophyte, were scattered at random through the argillaceous deposit in which some now lie prostrate. These appearances are represented in the section b, [fig. 281.], where the darker strata represent the Bradford clay, which some geologists class with the Forest marble, others with the Great Oolite. The upper surface of the calcareous stone below is completely incrusted over with a continuous pavement, formed by the stony roots or attachments of the Crinoidea; and besides this evidence of the length of time they had lived on the spot, we find great numbers of single joints, or circular plates of the stem and body of the encrinite, covered over with serpulæ. Now these serpulæ could only have begun to grow after the death of some of the stone-lilies, parts of whose skeletons had been strewed over the floor of the ocean before the irruption of argillaceous mud. In some instances we find that, after the parasitic serpulæ were full grown, they had become incrusted over with a coral, called Berenicea diluviana; and many generations of these polyps had succeeded each other in the pure water before they became fossil.
Fig. 282.
- a. Single plate or articulation of an Encrinite overgrown with serpulæ and corals. Natural size Bradford clay.
- b. Portion of the same magnified, showing the coral Berenicea diluviana covering one of the serpulæ.