Among the characteristic shells of the Inferior Oolite, I may instance Terebratula fimbria (Fig. 351), Rhynchonella spinosa (Fig. 352), and Pholadomya fidicula (Fig. 353). The extinct genus Pleurotomaria is also a form very common in this division as well as in the Oolitic system generally. It resembles the Trochus in form, but is marked by a deep cleft (a, Figs. 354, 355) on one side of the mouth. The Collyrites (Dysaster) ringens (Fig. 356) is an Echinoderm common to the Inferior Oolite of England and France, as are the two Ammonites (Figs. 357, 358).
Palæontological Relations of the Oolitic Strata.—Observations have already been made on the distinctness of the organic remains of the Oolitic and Cretaceous strata, and the proportion of species common to the different members of the Oolite. Between the Lower Oolite and the Lias there is a somewhat greater break, for out of 256 mollusca of the Upper Lias, thirty-seven species only pass up into the Inferior Oolite.
In illustration of shells having a great vertical range, it may be stated that in England some few species pass up from the Lower to the Upper Oolite, as, for example, Rhynchonella obsoleta, Lithodomus inclusus, Pholadomya ovalis, and Trigonia costata.
Of all the Jurassic Ammonites of Great Britain, A. macrocephalus (Fig. 360), which is common to the Great Oolite and Oxford Clay, has the widest range.
We have every reason to conclude that the gaps which occur, both between the larger and smaller sections of the English Oolites, imply intervals of time, elsewhere represented by fossiliferous strata, although no deposit may have taken place in the British area. This conclusion is warranted by the partial extent of many of the minor and some of the larger divisions even in England.
[1] Elements of Geology, 4th edition.
[2] I allude to several Zeuglodons found in Alabama, and referred by some zoologists to three species.
[3] See Phil. Trans. 1850, p. 363; also Huxley, Memoirs of Geol. Survey, 1864; Phillips, Palæont. Soc.