XVI FLORA OF OXFORDSHIRE. 
and western escarpments afford the most interesting bog plants 
in the county. Capping this formation is the Coral rag, which 
is largely composed of shells and corals, Isastrea and Fhecosmilia 
being especially frequent. The Coral rag with its associated 
beds, as it has been said, forms a tabulated area to the east of 
Oxford, the beds sloping gradually to the south at an angle of 
1°. In Berkshire it stretches in a nearly continuous band of 
variable width from Faringdon to Sandford and crossing the 
river into Oxfordshire joins the area stretching from Iffley 
north and eastwards. Its sudden disappearance at Wheatley is 
probably owing to an unconformable overlap of Kimmeridge 
Clay. The beds here are extensively quarried, and form an 
anticlinal dipping under the Kimmeridge Clay in every direc- 
tion from the centre. The beds are lowered by a fault which 
at Forest Hill brings the Lower Green Sand against the Coral 
Rag; at Holton the strata are overlapped by Kimmeridge 
Clay. The quarries at Headington have supplied much of the 
stone for building purposes in Oxford, Wadham College being 
one of the best examples, but the stone is not durable and 
should be laid so as not to expose the bedding planes. 
Kimmeridge Clay. This is a very stiff dark blue or olive- 
green clay, sometimes sandy and occasionally with bands of 
fossiliferous limestone. Its thickness in Oxfordshire is about 
100 feet, and it stretches in a very irregular outline from Sand- 
ford to Thame, forming flat pasture land about Toot Baldon, 
Cuddesdon, and Horspath. Its upper limits are much obscured 
by a thick drift deposit capping the higher ground from 
Wheatley to Thame. Crystals of selenite are not uncommon in 
it, and are frequent in the brick pits at Headington. Ostrea 
deltoidea is common. On Shotover its junction with the 
Portland Sands is marked by numerous springs, about which 
Drosera, Blysmus and other bog plants were formerly found. 
Portland Sands are some brownish sands resembling the 
calcareous grit, in structure differing in the peculiarly rounded 
lumps which the sandstone forms. It is well seen in a small 
quarry on Shotover Hill. The.beds are from 50 to go feet 
thick but make no great show in the county. They form the 
lower zone of the Shotover range, which may be considered to 
extend southwards as far as Garsington and Cuddesdon, The 
