
Parr III. Sxcr. i §2] JURASSIC. — 791 
Lower Oolitic period the estuary of the northern tract was submerged 
and a continuous sea-floor, that of the Cornbrash,. stretched Across 
England. | 
The Inferior Oolite attains its maximum development in the 
neighbourhood of Cheltenham, where it has a thickness of 264 feet. and 
consists of calcareous freestone and grit. It presents a tolerably copious 
suite of invertebrate remains, which resemble generically those of the 
Lias. The predominance of Rhynchonella and Terebratula over the rest 
of the brachiopods becomes still more marked. Gryphza, Lima, Pecten, 
Cardium, Myacites, Mytilus, Pholadomya, Trigonia are frequent shells, while 
ammonites and belemnites also occur, though much more sparingly than 
in the lias below, and in some of the later subdivisions of the Oolitic 

Fic. 386.—Lower OoLite AMMONITES. 
a, Ammonites (Stephanoceras) macrocephalus (Schloth.) (4); 6, A. (Cosmoceras) Parkin- 
soni (Sby.) (4); c, A. (Stephanoceras) Humphriesianus (Sby.) (4); d, A. (Harpoceras) 
Murchison (Sby.) G); e, A. (Harpoceras) opalinus (Rein) (3); jf, A. CLytoceras) 
torulosus (Zeit.) (4). 
series. Paleeontologically the Inferior Oolite has been subdivided into 
the following zones in descending order ?: 
Zone of Ammonites (Cosmoceras) Parkinsoni. 
(Stephanoceras) Humphriesianus. 
(Harpoceras) Sowerby?. 
(Harpoceras) Murchisone, 
29 29 
bb) ” 
29 9? 
_ Its component strata are subject to great variations in thickness and 
lithological character. The thick marine series of Cheltenham is reduced 
in a distance of 30 or 40 miles to a thickness of a few inches. The lime- 
stones pass into sandy strata, so that in Northamptonshire the whole of 
1 On the Ammonites of these zones, see S. S. Buckman, Q. J. Geol. Soc, 1881. p. 588. 
