Woolston. Among the fossils which they yield are Ammonites calloviensis, A. gowerianus, A. koenigi and Grypboea bilobata. The middle division, which comprises shales and clays with much pyrites, is characterized by Ammonites Jason, A. lamberti, Belemnites oweni and Cerithium muricatum ; the strata have been opened up along the Great Central Railway near Charndon, also near Winslow and at Fenny Stratford. The highest division, consisting of clays, contains Ammonites cordatus, Belemnites hastatus and great numbers of Grypbaea dilatata ; and it is well exposed in a brickyard by Quainton Road station.
CORALLIAN
Between the Oxford and Kimeridge Clays there is usually developed a series of sands and calcareous sandstones, oolitic limestones and coral beds, grouped as the Corallian formation. In Buckinghamshire these rock beds are not present in any conspicuous form ; they terminate north-east of Wheatley in Oxfordshire, and thence until we reach Upware in Cambridgeshire the formation is represented almost wholly by clay to which the name Ampthill Clay was given by Professor H. G. Seeley.
In the absence of the Corallian stone beds the probable equivalents have been shown on the geological survey map as extending through Shabbington, Ickford, Worminghall, Oakley and Boarstall, and thence from Dorton by Wescot to Quainton. Further on the Ampthill Clay outcrops between North Marston and Granborough, at Stewkley and onwards to the south of Linslade church.
The beds comprise dark clay and shale with selenite, and they contain Ammonites cordatus and var. excavates, A. plicatilis, A. vertebralis, Belemnites abbreviates, Gryphaea dilatata, Ostrea discoidea, and also Ostrea deltoidea.
There is a mingling of forms elsewhere belonging to the Oxford and Kimeridge Clays, and this is natural, as the conditions of deposition, in the absence of the Corallian rock beds, were more uniform ; but it is only by attention to the fossils that the division can be recognized. West of Boarstall a hard cherty band has been observed, which helps to form the gentle escarpment of Pans Hill. It has yielded Ammonites cordatus and A. vertebralis.[1]
KIMERIDGE CLAY
This clay formation extends from the Thame valley near Thame to the neighbourhood of Brill, Nether Winchendon and Waddesdon, and eastwards to Aylesbury, Quarrington, Hardwick, North Marston, Dunton and Stewkley. It occupies the lower grounds in a part of the celebrated vale of Aylesbury, which is diversified by numerous outlying hills of Portland and Purbeck Beds, with here and there coverings of Lower Greensand and Gault. It consists mainly of dark shale with occasional bands of septaria. In the lower beds Ostrea deltoidea is to be found, higher up Exogyra virgula is characteristic, and the upper beds contain
- ↑ Green, Geology of Banbury, etc. p. 44.
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