314 E. S. COBBOLD ON THE EXPOSED STRATA OP THE 



22. Notes on the Steata exposed in laying out the Oxford Sewage- 

 farm, at Sandfoed-on-Thames. By Edgar S. Cobbold, Esq., 

 F.G.S., Assoc.M.Inst.C.E. (Eead February 25, 1880.) 



The strata under consideration consist of the upper and middle 

 members of the Oxford Oolites, together with the Kimmeridge Clay ; 

 and though little novelty can be expected in a paper on such well- 

 studied and readily accessible deposits, it is hoped that at least one 

 or two important facts may be put on record. 



The area treated of is only about 1 J mile in length from east to west, 

 and one mile from north to south. It is situated about 4 miles S.E. of 

 Oxford, on the south side of the Thame and Aylesbury branch of 

 the Great Western Eailway, and east of the turnpike road from 

 Oxford to Dorchester & Henley. Though small, it presents some 

 interesting variations in the strata. 



Previous to the laying-out of the 350 acres selected for sewage- 

 irrigation, a number of trial-holes were dug to ascertain the nature 

 of the subsoils and substrata, and subsequently a complete system of 

 land-drainage was carried out, necessitating the digging of trenches 

 from 3 to 8 feet deep and not more than 66 feet apart all over 

 the land. There was therefore ample opportunity for obtaining 

 accurate information on the superficial development of the various 

 strata. 



At Headington a generalized section of the beds appears to be 

 somewhat as follows : — 



ft 

 Kimmeridge Clay. 



Coralline Oolite (say) 15 



Coral Eag (say) 15 



Sand 2 



Shell-bed 3 



Calcareous Grit 60 



Oxford Clay. 



In the neighbourhood of Sandford and Littlemore, the Coral Rag 

 and part of the Coralline Oolite are replaced by marls which are in 

 places full of small oysters and Serpulce, with a few other fossils, 

 but show no trace of corals*. These marls may be best seen in 

 the railway-cutting west of Littlemore Station, where they have 

 been thrown into long undulating curves, as shown in the section 

 (fig. 1), and have been traced to a distance of about one mile on all 

 sides. 



Northward they may be seen at an old quarry on the top of 

 Eose Hill, Iffley ; westward, at a small quarry behind the village 

 of Kennington',on the other side of the Thames valley ; southward, 

 in Sandford Hill; eastward, in the side of a small pond near the 



* One specimen of Tkecosmilia has been obtained on the sewage-farm, from 

 the lowest bed of the marls. 



