CORNBRASH
This formation consists of earthy and shelly limestone with marly or clayey bands, altogether from 5 to 8 feet in thickness. Among fossils Terebratula intermedia, Waldheimia obovata, Avicula ecbinata, Pholadomya and Ostrea flabelloides may usually be found. Although insignificant in thickness and of no economic importance in Buckinghamshire, the formation is of interest as being one of the more persistent bands in the Jurassic system.
North of Buckingham a large outlying mass of Cornbrash almost concealed beneath Oxford Clay and Glacial Drift occurs between Akeley and Thornborough. On the south side of the Ouse the formation extends from Barton Hartshorn to Tingewick, and eastwards from Beachampton, Bradwell, Great Linford and Newport Pagnell to near Newton Blossomville. Over much of the area the Cornbrash is concealed by Drift, and the broad outcrop is indefinite ; moreover it was extended more than it should have been on the geological survey maps by the inclusion of the Great Oolite Clays.[1] The formation is brought to the surface in inliers at Marsh Gibbon and West Stan Hill by an anticlinal structure which has disturbed and faulted the beds from Islip in Oxfordshire in a north-easterly direction. At Akeley north of Buckingham we again meet with an anticline with a northerly trend where the Cornbrash, Great Oolite Clay and Great Oolite Limestone have been bent into an arch, locally eroded, and exposed beneath the Kellaways Beds. [2]
OXFORD CLAY
As its name implies this is a great clay formation ; it occupies a vale chiefly of grass land with many dairy farms, and it forms part of a famous hunting country. It extends from Gawcott, Steeple Claydon, Grendon Underwood and Ludgarshall to Winslow, Whaddon Chase, Bletchley and. Fenny Stratford in the Ouzel valley, and thence to Chicheley and Astwood. The vale is an undulating one, rising at Knowl Hill between Edgcot and Middle Claydon into a conspicuous elevation, but the surface is modified by coverings of Boulder Clay and Drift Gravel, to the presence of which the scattered villages are to be attributed, as the gravels yield springs and furnish limited supplies of water to shallow wells. Many of these however have become polluted owing to defective sanitary arrangements, and deeper or distant supplies of water have to be looked for. The clay is locally dug for the manufacture of bricks, tiles and drain-pipes.
Resting on the Cornbrash there is usually about 10 feet of clay which is overlain by the yellow sands, sandstones and loams, all belonging to the Kellaways division, and about 20 or 30 feet in thickness. The lower beds are much better exhibited in the adjoining county of Bedford, but they have been exposed at Akeley, Padbury and Little
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