Ch. XX.] 



FOSSIL PLANTS OF GREAT OOLITE. 



411 



In the northwest 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 dim cult. A rich harvest of fossil ferns has been 

 obtained from the upper carbonaceous shales and sandstones at 

 Gristhorpe, near Scarborough (see figs. 422, 423). The lower 



Fig. 422. 



PieropTiyllum comptum. Syn. Cycadites eomptus. 

 Upper Sandstone and Shale, Gristhorpe, near Scarborough. 



Fig. 423. 



Hemitelites Broicnii, Goepp. Syn. Phlebopteris contigua, Lind. <fc Hntt. 

 Upper Carbonaceous strata, Lower Oolite, Gristhorpe, Yorkshire. 



shales are well exposed in the sea-cliffs at Whitby, and are chiefly 

 characterized by ferns and cycadese. They contain, also, a species 

 of calamnite, and a fossil called Equisetum columnare, which main- 

 tains an upright position in sandstone strata, over a wide area. 

 Shells of Estheria and JJnio, collected by Mr. Bean from these York- 

 shire 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 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 3-| feet thick, and there are several feet more of pyritous 

 coal resting upon it. 



