48 ME. A. M. DAVIES OS THE KIMEEID&E CLAY [Feb. I907, 



DlSCUSSIOX. 



Mr. H. B. Woodwaed congratulated the Author ou this con- 

 tinuation of his careful researches from lower to higher portions of 

 the Thame Yalley. Over most of the district now described the 

 Geological Survey had recently been engaged, in order to prepare 

 a map of the country around Oxford. The brickyard near Brill 

 was just beyond the confines of this area, but he had examined it 

 two years ago in company with Mr. Lamplugh, and together they 

 had obtained from the lowest strata then exposed, the ammonite 

 known as Cardioceras ecccavatum, GrypJiced dilatata, Ostrea dis- 

 coidea, and Serpida tetragona. These fossils, indicative of the 

 Ampthill Clay, had been identified by Mr. E. T. Newton, and the 

 record might be taken to supplement the observations of the Author. 

 "With regard to the Corallian area, Mr. T. I. Pocock had been 

 engaged in mapping the region of Studley and Arngrove, while he 

 (the speaker) had surveyed the ground near Wheatley and east- 

 wards. The cherty rock had proved a useful horizon at the base of 

 the Corallian in the northern region, and had been observed at 

 Stanton St. John and farther south. Elsewhere to the east the 

 boundary of Corallian Clay with Oxford Clay had been a matter of 

 difficulty, as the strata and occasional fossils were displayed only in 

 ditches and ponds. Although some modifications had been made 

 in the original geological survey by Mr. T. R. Polwhele, the changes 

 were made with the advantages of the labours of Blake & Hudle- 

 ston and of the 6-inch maps ; and Mr. Polwhele's field-work and 

 recognition of the clayey equivalents of the Corallian rocks were 

 deserving of all commendation. Along the eastern boundary there 

 was evidence, from well-sinkings, of bands of calcareous sandstone 

 that had probably been decomposed along the outcrop. Alluding 

 to the specimen exhibited, of Gryplicea dilatata with attached Ostrea 

 deltoidea from the Kimeridge Clay near Brill, he remarked that, 

 when these two came together, the bed in which they were found 

 was usually regarded as Corallian. Might not the GrypJicea have 

 been derived ? 



Prof. Hull said that he had listened with much interest to the 

 paper, and felt gratified that the work of the Geological Survey in 

 the Brill district had stood the test of the Author's examination. 

 That work had been carried out by Mr. Polwhele, and was rendered 

 specially difficult by the absence (except at the south-western 

 corner of the sheet) of the Corallian Oolite. Thus two forma- 

 tions of similar material (namely, bluish clay) were brought into 

 immediate contact in a country where there were few sections, 

 rendering it often impossible to decide where the boundary ought to 

 be drawn. In the district of Oxford, west of that surveyed by 

 Mr. Polwhele, the Corallian Oolite was sometimes present, as at 

 Heading'ton Hill, but in other places absent. This was the" case in 

 the south of the county near Earringdon, and here he had taken 

 the line of the Great Western Railway as the hypothetical boundary 

 between the Oxford and Kimeridge Clays, as the simplest and 



