132 MR. A. J. JUKES-BROWNE ON P^ a y 1906, 



8. The Clay-with-Flints ; its Origin and Distribution. By 



Alfred John Jukes-Browne, B.A., F.G.S. (Read January 10th, 



1906.) 



[Plate VI — Sections.] 



Contents. 



Page 



I. Definition and Theories of Origin 132 



II. Composition of the Clay-with-Flints 134 



III. Thickness of the Clay-with-Flints 137 



IV. Products of the Solution of Chalk 139 



V. Inferences to be drawn from the Distribution of the 



Clay-with-Flints 143 



VI. Summary and Conclusions 157 



I. Definition and Theories oe Origin. 



The peculiar deposit which has been termed ' Clay-with-Flints ' is 

 well known to most English geologists, as occurring in sheets or 

 patches of various sizes over a large area in the South of England, 

 from Hertfordshire on the north to Sussex on the south, and from 

 Kent on the east to Devon on the west. It almost always lies on 

 the surface of the Upper Chalk, but in Dorset it passes onto the 

 Middle and Lower Chalk, and in Devon it is found on the Chert- 

 Beds of the Selbornian Group. 



The existence of a red clay full of flints, lying as a soil or deposit 

 on the surface of the Chalk, was well known to geologists in the 

 middle of last century, such as Trimmer, Lyell, and Prestwich ; and 

 some appear* to have regarded it as a residue derived from the 

 solution and disintegration of the Chalk, but Joshua Trimmer in 

 1851 maintained that it and the other ' soils which cover the Chalk 

 of Kent ' were the result of aqueous transport. 1 



It was not until 1861 that it was described as a special accumu- 

 lation or aggregation by Mr. Whitaker, under the name of Clay- 

 with-Flints 2 ; and not until 1864 3 that he ventured to suggest 

 an explanation of its formation. His belief was and still is that 



' the Clay-with-Flints is of many ages, and may be forming even at the present 

 day, and that it is owing in great part to the slow decomposition of the Chalk 

 under common atmospheric action.' 



He holds that, as many Chalk-districts have been exposed to the 

 action of rain for thousands of years, much of the Chalk has been 

 carried away in solution, leaving the flints and the insoluble earthy 

 and ferruginous matter. He remarks that 



' To these would be added the clayey and loamy wash from the Tertiary lands, 

 and the remains of beds of that age left in pipes and hollows of the Chalk .... 



1 Quart. Journ. Geol. Soc. vol. vii (1851) p. 34. 



- ' Geology of Parts of Oxon & Berks' Expl. of Sheet 13, Mem. Geol. Surv. 

 p. 54. 



3 ' Geologv of Parts of Middlesex, Herts, &c. ' Expl. of Sheet 7, Mem. Geol. 

 Surv. p. 64. " 



