74 GASTEROPODA OF THE INFERIOR OOLITE. 
Deraits 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 foliowing is in the main an extract from ‘ Contributions to the 
Palwontology of the Yorkshire Oolites,” 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 Doacrr. Including the grey 
sands (Lingula-beds), 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 Nerinwa 
cingenda this band has been named the Nerinea-bed, 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 Murchisone-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 Mituerorn-Bep, which is best seen on the 
north horn of Cloughton Wyke at Sycarham, where the thickness may be about 
12 feet. This is alsoa 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. 
