Norton, and according to Mr. Beesley the Marlstone was 11 feet thick, while the underlying shaly and sandy beds were 16 feet in thickness. The lower beds yielded numerous fossils including fine specimens of Cypricardia.
North-west of Banbury the Marlstone rock bed is very well developed and forms a plateau which rises gradually from an altitude of 500 feet at that town to the famous escarpment of Edge Hill, 710 feet above sea-level. The rock forms a rich brown arable soil specially suitable for wheat growing. At Edge Hill the stone is a tough earthy limestone of brown and greenish hues, used for building, paving and road stone, and it has a thickness of 25 feet. There are large quarries on Burton Dassett Hill, a few miles to the north-east, while outliers of the beds occur at Bodington, Napton, and Upper Shuckburgh.
The Liassic sea now became deeper again, and we have the clayey series of the Upper Lias thrown down in the quiet waters. These beds consist chiefly of bluish-grey clay and shale with nodules of clayey limestone. The basement beds are pale earthy limestones, frequently nodular, and their junction with the Middle Lias is generally well marked. The organic remains include various fishes, and the ammonites A. annulatus, A. fibulatus, A. serpentinus and A. communis; belemnites occur, together with numerous bivalve shells, and several insects, notably some allied to the dragonflies.
Near Ilmington the thickness of the Upper Lias has been estimated by Mr. S. G. Hamilton at 120 feet; at the tunnel north of Chipping Norton, according to Mr. Beesley, it is about 36 feet, while near Banbury it increases to about 60 feet. It occurs in the form of numerous outliers and in valley bottoms northwards of Chipping Norton towards Tysoe, and Upper Lias fossils have been found by Mr. Brodie in crevices of the Marlstone rock bed on Edge Hill, while still farther north there is an outlier of Upper Lias, capped by Northampton Sands, on the hills near Burton Dassett.
At the close of the Liassic period a shallowing of the sea appears to have set in, caused presumably by movements of uplift; the climate was warm and the waters of the sea were favourable to the existence of vast numbers of aquatic animals whose remains make up a large part of the succeeding Oolitic rocks.
The Inferior Oolite Series is found in outlying patches near Ilmington and also in the south of the county along the eastern side of the Vale of Moreton. The series consists of two sub-divisions, the Midford Sands below and the Inferior Oolite above.
The Midford or Cotteswold Sands form a passage bed between the Lias and the Oolites; the materials of which they are made up and the fossils found in them exhibit a gradual change from the conditions which prevailed during the formation of the Upper Lias to those under which the Oolites were deposited. The beds, 30 to 150 feet thick, consist of
- 1Woodward, op. cit. pp. 221, 222.
- Woodward, op. cit. p. 270.