330 JURASSIC. 



is the same as that previously called Tetworth Clay by Sedgwick, 

 from Tetworth near St. Neots : this clay rests on the Elsworth 

 Rock in places, and is surmounted by the Boxworth Rock, a hard, 

 dark blue, flaggy and shelly limestone.' 



In Oxfordshire the Corallian Beds are exposed in the quarries at 

 Wheatley, and may be studied at Headington, Faringdon and other 

 places. The following divisions have been made : ^ — 



Feet 



Upper Calcareous Grit, consisting of variegated sand and clay 5 



Coral Rag and Coralline Oolite, oolitic shelly limestone and pisolite 10 to 30 

 Lower Calcareous Grit, hard grit and soft brown sands 20 to 80 



Fossils are most abundant in the Coral Rag division ; they 

 include Cidajis florigcmma ; and in places a Trigonia-bed with T. 

 perlata and T. Meriani is found. A Natica-bed with N. marcham- 

 ensis occurs in the Lower Calcareous Grit ; and in this division 

 Ammonites perarmatus is met with, and fine specimens occur in 

 the same beds at Marcham, Seend and Calne.^ At Studley, between 

 Islip and Brill, the Lower Calcareous Grit comprises sands with 

 a hard bed of calcareous grit at the base. 



In Wiltshire the Corallian Beds have been thus divided :^ — 



Feet. 



Upper Calcareous Grit, ferruginous sand and clay, slightly oolitic 20 



Coral Rag and Coralline Oolite, rubbly and shelly oolite, and 



pisolite, with beds of corals 120 



Lower Calcareous Grit, sands, and calcareous sandstone 25 to 50 



Sometimes a thick bed of clay overlies the Lower Calcareous 

 Grit. The beds are exposed at Highworth, Wootton Bassett, 

 Hillmarton, Calne, and Westbury. 



At Westbury the uppermost beds are of considerable economic 

 value, on account of the iron-ore which is developed directly under 

 the Kimeridge Clay. These beds contain Ammonites Berry en, A. 

 pseiidocordatiis, A. decipietis, Ostrea delfoidea, etc. 



At Steeple Ashton numerous Corals have been obtained, but 

 they have been collected chiefly from the ploughed fields, especially 

 from one field "on the north side of a road that turns off to the 

 south-east from the high road between Steeple Ashton and 

 Bratton."'^ 



In the Calne district Messrs. Blake and Hudleston observe that 

 " at Westbrook we have a fine coral reef, the first in our journey 

 northwards that we have been able to examine in situ. Layer upon 



^ Seeley, Index to Fossil Remains of Aves, etc. p. 109 ; Ann. Nat. Hist. (3), 

 X. loi ; Geologist, iv. 552 ; Blake and Hudleston, Q. J. xxxiii. 313 ; Bonney, 

 Cambridgeshire Geology, p. ii; Penning and Jukes-Browne, Geol. Cambridge 

 (Geol. Survey), p. 6 ; Green, Geol. Banbury, p. 45. 



2 Hull, Explan. Sheet 13 (Geol. Surv.), p. 5; Phillips, Geol. Oxford, p. 29S. 



^ Blake and Hudleston, Q. J. xxxiii. 301. 



* Lonsdale, T. G. S. (2), iii. 261 ; Hull, Explan. Sheet 34 (Geol. Surv.), 

 p. 20. 



^ Blake and Hudleston, Q. J. xxxiii. 286. 



