74 GASTEROPODA OF THE INFERIOR OOLITE. 



Details of the Yorkshire Basin (No. 4). 



The beds of Inferior Oolite age in this region are completely separated from 

 those to the south ; and their present outcrop is nearly at right angles to that of 

 the Cave Oolite and Lincolnshire Limestone. Although these arrangements are 

 probably mere accidents of stratigraphy, the result is the complete isolation of all 

 the Jurassic rocks of the basin of North-east Yorkshire. Since this is the case, 

 there can be no harm in reversing our previous practice of proceeding from the south 

 northwards, and in at once taking into consideration the important development at 

 Blue Wyke. The following is in the main an extract from ' Contributions to the 

 Palgeontology of the Yorkshire Oolites,' 1 describing the marine horizons or zones 

 of the Inferior Oolite, based chiefly upon the coast sections. 



1. First or lowest zone. — This is known as the Doggee. Including the grey 

 sands (Lingula-heds), the yellow sands, and the Dogger proper, a thickness of 

 80 feet may be assigned to the group, where most fully developed, as at Peak 

 (Blue Wyke). The remains of Gasteropoda are almost wholly confined to a shell- 

 bed 18 inches thick, which occurs about eight feet below the top of the series at 

 Peak, but nowhere else in Yorkshire. The matrix is very characteristic. The sub- 

 stance of the shells has been largely replaced by spathic iron, whilst their exterior is 

 lined with a thin skin of dark brown oxide. From the abundance of Nerincea 

 cingenda this band has been named the Nerinaa-loed, which is probably somewhere 

 about the horizon of the Pea-grit of the Cotteswolds, though not improbably it 

 contains species of a somewhat lower horizon. The Dogger in its totality may 

 be placed in the Opalinus-zone and lowest part of the Murchisonce-zone, and there 

 can be little doubt that Am. striatulus {radians) crosses the boundary into the 

 lower beds. Some 300 feet of " estuarine " sands and shales, with at best only 

 irregular traces of marine shells, succeed the Dogger, and then we arrive at — 



2. The second zone, known as the Millepoee-bed, which is best seen on the 

 north horn of Cloughton Wyke at Sycarham, where the thickness may be about 

 12 feet. This is also a kind of sandy ironstone, but more gritty and calcareous than 

 the Dogger. The Gasteropoda are mostly limited to one bed, whilst Conchifera 

 are abundant throughout. Some portions of the matrix contain more carbonate 

 of iron than of lime, and there is just sufficient iron peroxidized to impart a 

 reddish-brown tint to the mass, which is much flecked by a white substance allied 

 to kaolin. This peculiarity is less noticeable in the bed where the univalves are 

 mostly found. The Millepore-bed is well developed south of Scarborough, where 

 it becomes thicker. It forms an important scar in Gristhorpe Bay. In the 



1 ' Geol. Mag.,' dec. ii, vol. ix (1882), p. 148. 



