INTRODUCTION. xix 
Portland Stone is a white limestone, which is worked at 
Garsington. A second isolated area of Portland Stone occupies 
the high ground west of Great Haseley and Great Milton; 
another portion is found east of Thame. The Haseley quarries 
formerly yielded Ophrys aranifera. 
The iron sands capping Shotover are coloured on the Geo- 
logical Map as if they belonged to the Lower Greensand. 
Much controversy has taken place respecting them, some 
authorities suggesting that they are Purbeck beds, the top of 
the Jurassic system, but they are now more usually referred to 
the Wealden—a fresh-water formation, the occurrence in them 
of some fresh-water Crustacea supporting this theory. On the 
eastern side of Shotover, the sands (Wealden) rest on the Kim- 
meridge Clay without any Portland between them. These: 
sands are rich in vegetation, Gnaphalium sylvaticum, Ornitho- 
pus, Tanacetum, etc. occurring. 
The Cretaceous Formation. 
The Lower Greensand consists of an area extending from 
Culham to Burcott, and southwards to Clifton Hampden. Along 
the northern side the beds form an elevated ridge overlooking 
the Thames, and at Nuneham, where this ridge is well wooded, 
gives a scene of considerable beauty. East of Chiselhampton 
this formation is covered by an overlap of the Gault, but 
reappears at Albury and Great Haseley, the country between 
Albury and Thame being deeply covered with northern drift. 
Ammonites Deshayesii and Terebratula Silla occur in this 
formation. Jasione and Aspidium angulare are found on it. 
The Gault is a pale blue clay, about 200 feet thick ; and, 
unlike the distribution of the Lower Greensand, the Gault 
extends in an unbroken band across the country from Dorchester 
to the Bucks boundary near Thame. The ground formed by it 
is generally flat and marshy, and Rumeax maritimus occurs on it 
about Albury, and the Fritidlaria is found in its Thame 
meadows about Chiselhampton. 
The Upper Greensand extends parallel with the Gault. 
in a belt of variable width from Mongewell to Bensington, 
South Weston, and Chinnor to the Bucks border. 
ba 
