216 Dr. C. Callaway — Glacial Clay on Cotteswold Plateau. 



V. — The Ocourrenck of Glacial Clay on the Cotteswold 



Plateau. 



By C. Callaway, D.Sc, F.G.S. 



MR. L. EICHARDSON, F.G.S., having informed me that he had 

 seen gravels at a high level on the road leading from Stovvr- 

 on-the-Wold to Burford, I visited the locality, accompanied by 

 Mr. J. W. Gray, F.G.S. About 3i miles north of Burford, at the 

 corner of the turning to Taugley, we came upon a deposit of clay 

 with northern erratics in a quari-y of oolite. As the position of such 

 a formation was unexpected, and might be important, it seems 

 desirable to record the discovery. 



The Locality. — The deposit lies on the Cotteswold plateau, near 

 its eastern margin, about midway between Cheltenham and Oxford, 

 and about the same distance (18 miles) south-by-east of Meon Hill, 

 the most northerly spur of the Cotteswolds. The elevation is 

 approximately 650 feet above O.D., and 350 feet above the river 

 Evenlode, which lies 2^ miles to the east. The section is on a spur 

 of Oolite about 6 miles long, projecting from the mass of Tain ton and 

 Shipton Downs, to the north-north-west, and then curving round to 

 the north-west, rising towards its northerly termination to over 

 800 feet in Wyck Beacon. From the quarry the ground slopes 

 rather sharply in both directions, to the Evenlode on the east, to 

 a tributary of the Windrush on the west ; so that the clay lies on 

 the very apex of a pent-house ridge. 



The Clay. — The rock for which the quarry is worked is Great 

 Oolite. It has been excavated along a north and south line parallel 

 with the road for perhaps 50 yards, exposing a vertical section 

 whose maximum height is about 10 feet. The strata dip gently in 

 a westerly direction. The rock is much fissured, the fissures being 

 very irregular, so that at some points they broaden out at the top 

 into wide pockets, while in others they are little more than open 

 joints. Some of the narrow ones go down to the foot of the cliff". 

 All the fissures are packed tight with clay. It has found its way 

 not only down to the lower end of vertical fissures two inches wide, 

 but even horizontally into clefts of less than half of that width. 



The clay is stiff and hard. It is of two kinds, grey-blue and 

 brown, the former more compact and finer-grained than the other. 

 They are irregularly intermixed, without the faintest indication of 

 bedding or lamination. The difference of colour is original, and not 

 the result of chemical change subsequent to the intrusion of the clay. 

 This is seen in bulk-analysis and microscopic examination. 



The blue clay, triturated with water in a test-tube repeatedly, and 

 allowed to settle, appears to the naked eye an almost pure clay of 

 extremely fine texture. It gives no effervescence with acid. 

 Examined with a one-inch objective, the bulk of the material is still 

 seen to be very minute, but is mixed with a small proportion of 

 larger particles of two kinds, (1) brown sand and (2) very small 

 granules and microliths of clear minerals, some of which have a high 

 refractive index. 



