138 ME. A. J. JFKES-BKOWNE ON [May 1906, 



In the country round Luton its thickness is said to vary from 

 2 to 8 feet. The following is unpublished information. 



Near Weston, north-east of Hitchin, I saw a fairly-even spread 

 of dark reddish-brown Clay-with- Flints, from 1| to 3 feet in depth, 

 underlying loamy brickearth. 



Mr. C. J". Gilbert, F.G.S., informs me that, on the high ground 

 near Berkhampsted, there is much Clay-with-Flints, and that it is 

 often from 10 to 20 feet thick when not associated with brickearth ; 

 but that in many places brickearths, obviously derived from the 

 Reading Beds, lie in large potholes or solution-hollows which are 

 lined by a bed of clay and angular flints ; in such cases, the bed is 

 thin, and is sometimes only represented by a layer of black-coated 

 flints. 



I am informed by the Rev. E. C. Spicer, F.G.S., that several of 

 the cuttings on the Great Central Railway between Wendover and 

 Missenden show good sections of Clay-with-Flints, that its depth 

 varies from 1 to 6 or 7 feet, and that the average thickness might be 

 taken at about 3 feet. At the claypits near Walter's Ash, recently 

 described by Mr. Spicer, 1 the Clay-with-Flints forms a lining to 

 the large basins, which are filled with brickearth, gravel, and 

 sarsen-stones. 



Mr. Spicer informs me that, in other parts of the same district, 

 where the Clay-with-Flints forms a surface-deposit, its thickness 

 varies from 2 to 10 or 12 feet. In order to obtain some more 

 accurate idea of the average thickness at certain spots, he has been 

 kind enough to measure two sections for me. The first is near 

 Loosely Row, south of Risborough, where a cutting shows a wide 

 depression in the Chalk filled with the usual clay-deposit ; the 

 length of the depression is 25 yards, and its depth below the soil 

 in the centre is 10 feet, from which it lessens gradually on each 

 side to about 2 feet ; its average depth here, therefore, is 6 feet in 

 a length of 75 feet. 



The other locality is Denner Hill, south of Great Hampden, where 

 a slope is mantled by Clay-with-Flints, and, for a length of 440 yards 

 Avith a breadth of 200 yards, the depth of the clay is from 10 to 

 12 feet. This is an exceptional depth to be continuous over so large 

 an area, and especially on sloping ground. 



I have not been able to obtain any information as to the limits 

 within which the thickness of Clay-with-Flints varies over Hamp- 

 shire, for no observer seems to have paid much attention to it in 

 that county, except to the north of Chichester (Sheet 317), where 

 it has been mapped by Mr. C. Reid. JN"o actual measurements of it 

 are given in the Explanation of that sheet, but Mr. Reid observes 

 that ' the total thickness seldom reaches 10 feet ' (op. cit. p. 38). 



From the particulars now given it is clear that any theory of the 

 formation of Clay-with-Flints must be equal to accounting for its 

 accumulation to a thickness of 3 or 4 feet over large areas. 



1 Quart. Journ. Geol. Soc. vol. lxi (1905) p. 39. 



