Vol. 6 2. J THE CLAT-WITH-FLINTS. 161 



reduced to the state now presented by the masses- of so-called 

 ' brickearth.' Much of what has been mapped as Clay-with-Flints 

 has probably been formed from the further disintegration and 

 detrition of these brickearths, accompanied by solution of the chalk 

 upon which they rest. Take, for instance, such a tract of Clay-with- 

 Flints as that around Aldworth and Ashampstead (see p. 147) : the 

 existing Eocene outliers are evidently those portions of a larger 

 mass that escaped reconstruction during the Glacial Epoch ; the 

 surrounding and intervening tract of Clay-with-Flints consists of 

 the remains of the disintegrated portions of the same Eocene 

 deposits, mingled with materials which have travelled from the 

 higher ground on the north and north-west. 



The enclosure of unbroken chalk-flints in the clay could only 

 take place where the rain had easy access to the underlying Chalk. 

 This would, at first, be chiefly round the periphery of such a tract ; 

 but afterwards it would occur at places within the area where 

 mechanical erosion had left only a small thickness of clay-cover, 

 or where a growth of large trees had sent their roots through the 

 base of the Eocene into the Chalk. Thus, under the continued 

 action of rain, both mechanical and chemical, such a tract would 

 diminish in size and thickness, and would be intersected by rain- 

 channels, some of which would eventually cut down to the Chalk. 

 It seems easy to imagine a continuance of this process until the 

 whole mass was reduced to its present state, when it consists partly 

 of displaced masses of Eocene clay and sand, partly of residual 

 Clay-with-Elints : the whole having sunk down irregularly into the 

 Chalk, until parts of it are 30 or 40 feet below the inclined plane 

 upon which the Eocene outliers rest. 



While, therefore, I do not deny that some of the material which 

 now enters into the composition of the Clay-with-Flints may be 

 Eocene detritus collected in the Miocene or Pliocene Periods, 

 I think that the accumulation, as we now find it, is the 

 result of a special set of processes which were in 

 operation during late Pliocene and early Pleistocene 

 times. In more recent times, I think that there has been little 

 accession of material to the Clay-with-Flints, except by a limited 

 solution of the Chalk. Post-Glacial erosion must have destroyed a 

 great deal of it, by widening all the valleys at the expense of the 

 intervening ridges, until what were formerly large tracts of Clay- 

 with-Flints have been reduced to the condition of small patches 

 scattered over an area of bare chalk. 



In conclusion, I gratefully acknowledge the assistance afforded 

 me by Mr. William Hill, F.G.S., who has devoted much time and 

 care to the weighing experiments and to the estimation of the 

 residue from several samples of chalk. I also desire to thank 

 Mr. H. J. Osborne White, F.G.S., for much useful information, as 

 well as for specimens of chalk and Clay-with-Flints from near 

 Wargrave. For other specimens and information I am indebted to 

 Mr. Charles Griffith, F.G.S., Mr. C. J. Gilbert, F.G.S., Mr. J. Saunders, 

 and the Rev. E. C. Spicer, F.G.S., as mentioned in the foregoing pages. 



