A HISTORY OF BUCKINGHAMSHIRE 



the consequent formation of sulphate of lime, which was deposited along 

 the open planes of bedding and in crevices of the fractured rock. 1 



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, Laven- 

 don and Olney, also at Clifton Reynes, Emberton and Sherington. At 

 Gayhurst many fossils were formerly collected by J. H. Macalister. 2 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 circum- 

 stances the strata would hold a good deal of water, although free circula- 

 tion 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 Osfrea 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 GREAT OOLITE CLAY 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. 3 It was mentioned by Buckland that shelly limestone 

 obtained at Buckingham had been used for ornamental purposes under 

 the name of Buckingham Marble 4 ; 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 Osfrea 

 sowerbyi and O. subrugulosa. Thus at Bradwell beneath the Cornbrash 

 and above the Great Oolite Limestone there is about 1 3 feet of marly 

 clays, variegated in colour, with sand and marly limestone crowded with 

 Osfrea, 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, notice- 

 able along the gentle scarp to the south of the Ouse valley between 

 Buckingham and Newport Pagnell. 



1 ' Lower Oolitic Rocks of England,' Geol. Survey, p. 393. 2 Geologist, iv. 215, 486. 



8 Geology of the country around Banbury, Woodstock, Bicester and Buckingham, p. 28 (1864). 

 4 Ann. Phil. ser. 2, i. 464 (1821). 



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