ODLING : CORRELATION OF THE UPPER AND MIDDLE OOLITES 277 
undergoes remarkable changes. In the region round Studley and 
Arngrove we find a local facies of Lower Corallian in the form of a 
chert " largely composed of the spicules of a sponge (Rhaxella) which 
is also common in the Lower Calcareous Grits of Yorkshire. This 
facies has been named the Rhaxella Chert or Arngrove Stone by Dr. A. 
Morley Davies,* and appears to occur at the base of the Calcareous 
Grits in this region only. I 
The Upper Corallian is for the most part represented by " Coral 
Rag," usually resting on sandy beds with a pebble bed below, but on 
tracing it to the east of Oxford, we find rapid changes. At Stowood, 
Headington and Shotover, and to the west of this line, typical coral 
reef material exists, but to the east it is not seen in any of the quarries. 
Near Woodperry, Stanton St. John and Wheatley, the rock consists 
of detritai calcareous material with few perfect fossils ; at Lye Hill 
a few beds of clay appear, and east of this the calcareous facies rapidly 
gives place to an argillaceous facies, the Ampthill Clay. 
The only exposure at present showing the junction of the Kim- 
eridge Clay with the underlying Corallian occurs on Shotover ; here, 
in contrast to the Weymouth district, there is a sharp break between 
the two, the clay resting on an eroded water-worn surface of the 
limestone, all the Supra-Corallian of Weymouth being absent. 
The junction of the Kimeridge with the Portland is usually 
hidden by slips, but wherever the uppermost beds are exposed, the 
Kimeridge Clay becomes somewhat arenaceous, showing a transition 
into the Portland sands above. This is especially the case in the 
Culham brickyard, where the mammilatus beds of the Gault rest directly 
on the Kimeridge Clay ; these uppermost beds of the Kimeridge 
Clay may, however, be of Hart well Clay age. 
In this district, the Portland series is largely arenaceous, but 
locally the upper beds are sufficiently cemented with calcareous 
material to form a " roach," the Trigonia roach " bed of Portland, 
for instance, being readily recognizable at Wheatley. 
Locally there occurs a well marked pebble bed of lydites and 
phosphatized bones separating the Upper Portland from the Lower 
* Quart. Journ. Geol. Soc, Vol. LXIIL, 1907, pp. 37, 38. 
t The Lower Calcareous Grits of Filey Brig also contain an abun- 
dance of spicules of Rhaxella. 
