The Inferior Oolite of Yorkshire consists largely of shales and sandstones, which assume much the aspect of a true coal-field, thin seams of coal having actually been worked in them for more than a century. A rich harvest of fossil ferns has been obtained from them, as at Gristhorpe, near Scarborough (Fig. 350). They contain also Cycadeæ, of which family a magnificent specimen has been described by Mr. Williamson under the name Zamia gigas, and a fossil called _Equisetum Columnare_ (see Fig. 397), which maintains an upright position in sandstone strata over a wide area. Shells of _Estheria_ and _Unio,_ collected by Mr. Bean from these Yorkshire coal-bearing beds, point to the estuary or fluviatile origin of the deposit. Fig. 350: Hemitelites Brownii. At Brora, in Sutherlandshire, a coal formation, probably coeval with the above, or at least belonging to some of the lower divisions of the Oolitic period, has been mined extensively for a century or more. It affords the thickest stratum of pure vegetable matter hitherto detected in any secondary rock in England. One seam of coal of good quality has been worked three and a half feet thick, and there are several feet more of pyritous coal resting upon it. Fig. 351: Terebratula fimbria. Fig. 352: Rhynchonella spinosa. Fig. 353: Pholadomya fidicula. 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). Fig. 354: Pleurotomaria granulata. Fig. 355: Pleurotomaria ornata. Fig. 356: Collyrites (Dysaster) ringens. Fig. 357: Ammonites Humphresianus. Fig. 358: Ammonites Braikenridgii. Fig. 359: Ostrea Marshii. 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. Fig. 360: Ammonites macrocephalus. 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.