xi. GROUPS OF STRATA. 139 



Burford, and about Stonesfield, the whole thickness is but one- 

 fourth of that near Cheltenham. This arises from the great re- 

 duction of the Inferior oolite, from two or three hundred feet to 

 less than twenty, and from the absence or extreme attenuation 

 of the fuller's-earth c . 



Thus, on the side of the Evenlode valley, we have about TOO feet 

 of strata, viz. : 



Cornbrash . . . . . . . . 8 to 10 feet. 



Forest marble with accompanying clays . . . 20 to 30 feet. 

 Great oolite white -i 



marly 1> . . . . 40 to 60 feet. 



flaggy and sandy J 

 (Occasional clay bed.) 

 Inferior oolite . 10 to 20 feet. 



The lower part of the Great oolite is the famous bed of Stones- 

 field slate. 



Now passing north-eastward to the valley of the Cherwell, we 

 find about Steeple-Aston and Deddington a similar series, with the 

 addition of a band of ironstone at the bottom, but no true Inferior 

 oolite. 



The series reads thus : 



Cornbrash 8 to 10 feet. 



Forest marble 20 to 30 feet. 



Great oolite white \ 



marly . . . .50 feet. 



flaggy and sandy ) 

 (Occasional clay bed.) 

 Ironstone band . i to 8 feet. 



The facts thus collected agree with the opinion unanimously 

 adopted by the National Survey in their maps and sections, viz. 

 that the true Inferior oolite is extinct in the region north of 

 Oxford, as well as the fuller's-earth beds. The iron-bands, however, 

 at the base of the whole series, have come by degrees to be re- 

 cognized as coeval with those which are the lowest beds of the 

 Inferior oolite series of Northamptonshire, Lincolnshire, and York- 

 shire. This can hardly be doubted as we proceed in our examina- 

 tion eastward and north-eastward. 



c The clay bed often recognized above the iron bands and sands associated with 

 them, and sometimes observed below the Stonesfield slate, may be regarded as the 

 continuation or representative of the fuller's-earth. 



