xvi FLORA OF OXFORDSHIRE. 
outliers, one at Islip and one at Middleton; in the latter place 
it is associated with Cephalanthera pallens. Clematis vitalba, 
Carduus eriophorus and Brachypodium pinnatwm are also 
frequent on the Oolite. : 
Forest Marble. This sub-formation of the Great Oolite is 
so-called from its occurrence in Wychwood Forest, of which it 
forms a large portion. It consists of hard, flaggy limestones, 
much ripple marked and often formed of broken oyster shells 
cemented together by carbonate of lime. It is about 25 feet 
thick and from Wychwood the outcrop of the rock runs 
between the plateau of Great Oolite and Cornbrash to Bucknell, 
where it is cut off by a fault bringing up the Great Oolite. 
There is a large outlier in Blenheim Park and another at 
Dornford ; near Tadmarton a portion is let down into the Great 
Oolite by a fault. Thin inliers are seen in the brook courses 
north of Bicester and the formation is also seen in the centre 
of the inliers of Cornbrash at Islip and Oddington. South- 
wards towards Witney it becomes very thin and reaches its 
southern exposure at Brize Norton. 
Cornbrash. This, the higher formation of the Lower Oolite, 
consists of a group of limestones from 6 to 15 feet thick, very 
regular in its bedding and as constant in its occurrence as the 
Forest Marble is erratic. The limestones are either rubbly 
or solid. In colour they are blue internally, but weather to 
a cream colour or brown. The arable land where this rock 
forms the subsoil is of a deep reddish-brown colour. Its typical 
fossil is the pretty Avicula echinata. The outcrop of the Corn- 
brash runs from Brize Norton by Witney in a narrow strip to 
Woodstock, where it broadens out northwards so as to take in 
Tackley, narrowing to a few hundred yards as it crosses the 
Cherwell, after which it again widens to 2 or 3 miles from 
Kirtlington by Bicester to Fringford, forming a flat uninteresting 
country. A curious row of inliers brought up along an anti- 
clinal line stretching far eastwards occur as dome-shaped masses 
rising out of the flat dull plain of the Oxford clay and on these 
inliers the villages of Islip, Oddington, Chesterton, Merton, and 
Ambrosden have been built. The arable land on the Cornbrash 
is well adapted to the growth of wheat. Few characteristic 
plants occur. 
