§ 34. ZOOPHYTES OF THE JURASSIC FORMATION. 639 



and been able to expand and contract.* This opinion is based on the 

 circumstance, that some specimens occur in which the zoophyte is in 

 the form of a nearly flat circular disk, and others in that of a sub- 

 cylindrical pouch ; in the former state, the outer reticulated structure 

 is elongated, while in the latter, it is contracted and corrugated. The 

 polype-cells are cylindrical and very regular ; the flints often present 

 beautiful casts of them, which appear like rows of minute pillars on 

 the inner surface." f 



When the flint that fills up the cavity of a Ventriculites 



can be extracted, it is a solid cone, having its surface 

 studded over with papillae, which are casts of the orifices 

 of the polype-cells. When the enclosed polyparia in flint 

 nodules have perished, chalcedony, and quartz crystals, and 

 sometimes crystallized pyrites, are found filling up, more 

 or less completely, the cavities left by the decayed parts of 

 the zoophyte, ij; 



34. Zoophytes of the Jurassic formation. — The 

 Oolite, as we have previously remarked, abounds in corals, 

 and contains beds of limestone which are merely coral- 

 reefs that have undergone no change but that of elevation 

 from the bottom of the deep, and the consolidation of their 

 materials. The Coral-rag, in fact, presents all the cha- 

 racters of modern reefs ; the polyparia belong to Astrcecp, 

 Caryophyllice, JMadrejwrce, 3feandrincp, and other genera 

 which principally contribute to the formations now going 

 on in the Pacific. Shells, echini, teeth and bones of fishes, 

 and other marine exuviae, occupy the interstices between 

 the corals, and the whole is consolidated by sand and 

 gravel, held together in some instances by calcareous, in 



* As in the Flustrae and Pennatulae previously described (ante, 

 p. 610). 



f See Op. cit. pp. 269—278. 



J I beg to refer to my paper on a " Microscopic Examination of 

 Chalk and Flint/"' published in Ann. Nat. Hist. 1815: and "Gee- 

 logical Excursions round the Isle of Wight;" pp. 179 — 1S4, for a par- 

 ticular account of the silicification of these and other zoophytes. 



