350 
ELEMENTS OF GEOLOGY. 
Fig, 850. 
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, n e a r 
Scarborough (Fig. 
350). They contain 
also Cycadeae, of 
which family a 
magnificent speci¬ 
men has been de¬ 
scribed by Mr. Wil¬ 
liamson under the 
Hemitelites Brownii, Goepp. Syn. Phlehopteris contigua^ 
Lind, and Hutt. Lower carbonaceous strata, Inferior 
Oolite shales. Gristhorpe, Yorkshire. 
name Zamia Gigas, 
Golumnare 
and a fossil called Equisetmn Golumnare (see Fig. 397, p. 
376), which maintains an upright position in sandstone strata 
over a wide area. Shells of Estheria and collected by 
Mr. Bean from these Yorkshire coal-bearing beds, point to the 
estuary or fluviatile origin of the deposit. 
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 exten¬ 
sively for a century or more. It afibrds 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^ Sow. 
Inferior Oolite marl. 
CotsWold Hills. 
Fig. 852. 
Rhynclionella spinom, 
Schloth. Inferior 
Oolite. 
Fig.858. 
Pholadomya Jidicula, Sow. 
One-third natural size. 
Inferior Oolite. 
Among the charkcteristic shells of the Inferior Oolite, I 
may instance Terebratula fimbria (Fig. 351), Ehynchonella 
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 Troehus in form, but is marked by a deep 
cleft (a. Figs. 354,355) on one side of the mouth. The Go% 
