Different species of crinoids, or stone-lilies, are also common in the same rocks with corals; and, like them, must have enjoyed a firm bottom, where their base of attachment remained undisturbed for years (_c,_ Fig. 330). Such fossils, therefore, are almost confined to the limestones; but an exception occurs at Bradford, near Bath, where they are enveloped in clay sometimes 60 feet thick. 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 encrinite, were scattered at random through the argillaceous deposit in which some now lie prostrate. These appearances are represented in the section _b,_ Fig. 330, where the darker strata represent the Bradford clay, which is however a formation of such local development that in many places it cannot easily be separated from the clays of the overlying “forest-marble” and underlying “fuller’s earth.” 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 bryozoan, called _Diastopora diluviana_ (see _b,_ Fig. 331); and many generations of these molluscoids had succeeded each other in the pure water before they became fossil. Fig. 330: Apiocrinites rotundus, or Pear Eucrinite. Fig. 331: a. Aingle plate of body of Apiocrinus, overgrown with serpulæ and bryozoa; b. Portion of same magnified, showing the bryozoan Diastopora diluviana covering one of the serpulæ. We may, therefore, perceive distinctly that, as the pines and cycadeous plants of the ancient “dirt-bed,” or fossil forest, of the Lower Purbeck were killed by submergence under fresh water, and soon buried beneath muddy sediment, so an invasion of argillaceous matter put a sudden stop to the growth of the Bradford Encrinites, and led to their preservation in marine strata.