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 Rh the consequent formation of sulphate of lime, which was deposited along the open planes of bedding and in crevices of the fractured rock.

Beyond Wolverton the Great Oolite extends northwards from Castlethorpe to Hansthorpe and along the borders of Salcey Forest; it appears in the Ouse valley at Gayhurst, Ravenstone, Warrington, Lavendon and Olney, also at Clifton Reynes, Emberton and Sherington. At Gayhurst many fossils were formerly collected by J. H. Macalister. In this region the stone layers are much jointed and fissured and the walls of the fissures are seen to be water-worn. Under favourable circumstances the strata would hold a good deal of water, although free circulation is liable to be arrested by the partings of marl.

In the south-west of England and northwards as far as Bicester in Oxfordshire the Great Oolite is surmounted by beds of clay, sands and fissile oolitic and shelly limestone grouped as the Forest Marble, so named from the occurrence of the strata in the forest of Wychwood east of Burford in Oxfordshire, where in old times the stone was employed for chimney pieces.

On Blackthorn Hill south-east of Bicester we find the last definite representative of Forest Marble type, about 18 feet in thickness and comprising clays with a band of tough blue shelly oolite, with masses of lignite and greenish marly galls. Here one of the characteristic fossils Waldheimia digona is to be found, together with Ostrea and Acrosalenia. The upper beds comprise pale greenish grey clays which indicate the incoming of the estuarine conditions which prevailed in the area to the north-east where the term is usually applied.

East of Tingewick and again at Thornton Prof. A. H. Green noted a hard limestone similar to that above mentioned. It is overlain by blue and white marly clays and these occasionally contain calcareous bands and concretions. It was mentioned by Buckland that shelly limestone obtained at Buckingham had been used for ornamental purposes under the name of Buckingham Marble .; but the stone may have been obtained from one of the shelly bands at top of the Great Oolite Limestone. At Buckingham the Great Oolite Clay is about 1 5 feet in thickness, but northwards at Akeley it is less developed. Here we find grey and black clay and marl, while in some localities there is greenish clay with Ostrea sowerbyi and O. subrugulosa. Thus at Bradwell beneath the Cornbrash and above the Great Oolite Limestone there is about 13 feet of marly clays, variegated in colour, with sand and marly limestone crowded with Ostrea, and at the base much ferruginous matter. Here we have the type of the Great Oolite Clay of the midland counties, a formation of uncertain thickness and varying character.

Where exposed this clayey series forms a wet tenacious soil, noticeable along the gentle scarp to the south of the Ouse valley between Buckingham and Newport Pagnell.