324 JURASSIC. 



with in a deep well-sinking at the Great Western Railway-works, 

 Swindon : there the overlying Oxford Clay was 510 feet thick.^ 



The Oxford Clay forms a broad tract of low-lying country from 

 Chippenham and Wootton Bassett to Purton, Cricklade, Lechlade, 

 and Oxford. South of Cirencester, the Kellaways Rock is 

 represented by yellowish sands and calcareous sandstone, highly 

 fossiliferous in places.^ The best section of the Rock that has 

 been exposed in the South of England is that opened up in the 

 railway-cutting north of South Cerney, and which has been de- 

 scribed by Prof. Allen Harker.^ Here the sands contain huge con- 

 cretionary masses or "doggers" of calcareous sandstone, much 

 like those in the Corallian beds (Bencliff grits) near Weymouth. 

 The Kellaways Rock occurs also near Malmesbury. 



Near Oxford, according to Prof. Phillips, we have the' following 

 succession of Ammonites in the Oxford Clay : * — 



4. Ammonites vertebralis. 



3. Lambert i. 



2. Dnucani {yason). 



I. Kellaways Rock, etc., of Wiltshire. 



The Kellaways Rock, however, is not known in Oxfordshire, 

 although some of its characteristic Ammonites have been found in 

 the lower part of the Oxford Clay. The Oxford Clay is exposed 

 in the St. Clement's Pits. It extends from Oxford (300 feet) by 

 Fenny Stratford to Bedford, Kimbolton, and Huntingdon, and 

 forms the substratum of much of the western portion of the 

 Cambridgeshire fens and those which border on Huntingdonshire. 

 It may be studied at Eynsbury, St. Neots, and in brick-pits near 

 St. Ives. A bed of rock which has been noticed by Prof. Seeley at 

 St. Neots may be on the horizon of the Kellaways Rock.^- This 

 rock has also been observed near Wellingborough. 



In the Northampton district Prof. Judd has noted the following 

 principal divisions in the Oxford Clay : '^ — 



6. Clays with Ammonites of the group of the ' Cordati.'' 



5. Clays with Ammonites of the group of the ' Ornati.' Dark-blue clays with 



much iron-pyrites, and pyritic Ammonites. A, ornattis, A. Dimcani, 



A. a thief a. 

 4. Clays witli Beieimiites hastaitis. 

 3. Clays witli Belcmitites Oweiiii. Gryphaa dilatata appears to commence in 



tlaese beds. 

 2. Laminated blue shales with Nnciila nuda and compressed Ammonites . 

 I. Kellaways Sands, Sandstones, and Clays, with Grypha:a bilobata, Avicula 



inccqiiivaivis, and Belevinites Ozuenii. 



1 Q. J. xlii. 287. 



"^ E. Hull, Explanation Sheet 34 (Geol. Survey), p. 19. See also J. Buckman, 

 Q. J. xiv. 125. 



2 Proc. Cottesw. Club, 1883-S4, p. 176. 

 * Geol. Oxford, p. 298. 



^ Geologist, iv. 553 ; see also T. G. Bonney, Cambridgeshire Geology, p. 10; 

 Penning and Jukes-Browne, Geol. Cambridge (Geol. Survey), p. 5. 



" Geol. Rutland, etc., p. 232 ; see also Dr. H. Porter, Geology of Peterborough, 

 1861. 



