A Manual of Elementary Geology / or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments

by Sir Charles Lyell

Pterophyllum comptum. (Syn. Cycadites comptus.) Upper sandstone and shale, Gristhorpe, near Scarborough.

In the north-west of Yorkshire, the formation alluded to consists of an upper and a lower carbonaceous shale, abounding in impressions of plants, divided by a limestone considered by many geologists as the representative of the Great Oolite; but the scarcity of marine fossils makes all comparisons with the subdivisions adopted in the south extremely difficult. A rich harvest of fossil ferns has been obtained from the upper carbonaceous shales and sandstones at Gristhorpe, near Scarborough (see [figs. 295], [296.]). The lower shales are well exposed in the sea-cliffs at Whitby, and are chiefly characterized by ferns and cycadeæ. They contain, also, a species of calamite, and a fossil called Equisetum columnare, which maintains an upright position in sandstone strata over a wide area. Shells of the genus Cypris and Unio, collected by Mr. Bean from these Yorkshire coal-bearing beds, point to the estuary or fluviatile origin of the deposit.

Fig. 296.

Hemitelites Brownii, Goepp. Syn. Phlebopteris contigua, Lind. & Hutt. Upper carbonaceous strata, Lower Oolite, Gristhorpe, Yorkshire.

At Brora, in Sutherlandshire, a coal formation, probably coeval with the above, or 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 3¹/₂ feet thick, and there are several feet more of pyritous coal resting upon it.

Inferior Oolite.—Between the Great and Inferior Oolite, near Bath, an argillaceous deposit called "the fuller's earth," occurs, but is wanting in the north of England. The Inferior Oolite is a calcareous freestone, usually of small thickness, which sometimes rests upon, or is replaced by, yellow sands, called the sands of the Inferior Oolite. These last, in their turn, repose upon the lias in the south and west of England.

Among the characteristic shells of the Inferior Oolite, I may instance Terebratula spinosa ([fig. 297.]), and Pholadomya fidicula ([fig. 298.]). 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 singular cleft (a, [fig. 299.]) on the right side of the mouth.