278 ODLING : CORRELATION OF THE UPPER AND MIDDLE OOLITES 
Portland.* Blake remarks that this does not occur at a constant 
horizon, but H. B. Woodwardf considers that the evidence of Blake's 
lists of fossils does not uphold this conclusion, and considers that such 
a marked lithological break extending over a large area is most likely to 
occur at a constant horizon. The beds of this age have been described 
in some detail by Dr. A. Morley Davies, who also appears to agree with 
Woodward. J 
On tracing this series eastwards it is found that the Lower Portland 
becomes more argillaceous, finally passing into the Hartwell Clay in 
the neighbourhood of Aylesbury, while to the south-west it is represented 
by the Swindon Clay. This, the Hartwell and Swindon Clay, appears 
to include some of the upper beds of the Kimeridge Clay as well as 
the Lower Portland, and constitutes a facies of its own. A similar 
condition is found in the Boulonnais. 
In the neighbourhood of Wheat ley and Brill sandy and marly 
beds have been described by Fitton§ as being of Purbeck age, and this 
identification has been verified by Morley Davies. The Purbeck on 
Shotover, however, does not appear to have been rediscovered.! | 
In the neighbourhood of Upware, near Cambridge, the occurrence 
of Upper Corallian in the form of a true Coral Rag is remarkable, 
occurring as it does as an apparently isolated patch. Below comes the 
Ampthill Clay with Elsworth Rock at the base, resting on Oxford Clay. 
In Lincolnshire we find the Kimeridge Clay Well developed at 
Market Rasen, while the Portland and Purbeck may in part be re- 
presented by the Spilsby Sandstone, which is considered to be equivalent 
to the Belemnites lateralis Beds of Speeton.** 
Of the Yorkshire or North Country district, the valuable memoir 
by Fox Strangwaysff renders certain facts quite clear. First, the 
* Dr. Salfeld places the Lydite pebble bed of Swindon in the middle 
of the Lower Portland, as recognized in England, zone of P. eastlecot- 
tensis. Quart. Journ. Geolog. Soc, Vol. LXIX., p. 424. 
t Geolog. Survey Memoir, Jurassic Rocks of Britain, Vol. V. 
X Proc. Geol Assoc., Vol. XVL, p. 25. 
§ Observation on Strata between the Chalk and the Oxford Oolites. 
II Proc. Geol. Assoc., Vol. XVL, p. 38 et seq. 
** Lamplush, Quart. Journ. Geol. Soc, Vol. XLV., pp. 575-615. 
ft Geol. Snrvej^ ]\Iemoir, Jurassic Bocks of Great Britain, Vol. I. 
