276 ODLIXG : CORRELATION OF THE UPPER AND MIDDLE OOLITES 
The Kimeridge Clay, which succeeds, calls for no special note. 
The village of Kimeridge, from which it takes its name, being in the 
immediate neighbouvhood, the sections are the type sections. The 
general succession will be most readily seen by reference to Plate 
XXIX., which shows the correlation between the AVeymouth and 
Boulonnais districts. 
At the top of the Kimeridge Clay, and insensibly passing up from 
it, come the Portland Sands, capped by Portland Stone, forming the 
Lower and Upper Portlandian of the district. The separation, though 
purely litliological and probably not occurring at a constant horizon, 
is- valuable for mapping purposes. Above come the Purbeck Beds, a 
series of land, freshwater and estuarine beds, which seem to link the 
Jurassic with the Cretaceous. All these last beds are best studied in 
the Isle of Portland, with the exception of the Portland Sands, which 
are more accessible at Ringstead Bay. 
Turning now to the Oxford district — with wliich is included 
not only the immediate vicinity of Oxford, but also some of the more 
easterly outcrops — we find many marked differences: The thicknesses 
of the beds have all enormously decreased. 
Starting with the Cornbrash, we find that a lower horizon has come 
in, marked by an abundance of Terebratula interniedia. Of the Kella- 
ways Beds tliere appears to be no definite representation, unless certain 
somewhat sandy beds at the base of the Oxford Clay in part represent 
them. The junction of the Calcareous Grits with the Oxford Clay is 
nowliere accessible, but the information afforded by well-borings, etc., 
gives no suggestion of alterations of clay and sandstones representing 
the Nothe Grits and Nothe Clays of the Weymouth district. 
The Corallian in the neighbourhood of Oxford is usually divided 
into an Upper, or Coral Rag, and a Lower or Calcareous Grits. This 
classification, though useful tor mapping purposes, is unfortunate since 
the base of the Upper Corallian is thus often included in the Calcareous 
Grits. The junction between the Upper and Lower Corallian is re- 
presented by a band characterized by a mixture of Lower and Upper 
Corallian forms, and containing numerous pebbles, chiefly of chert, 
quartz and jaspedeous cherts. Passing eastwards from the neighbour- 
hood of Oxford the Corallian, v\nth a total thickness of about 100 feet. 
