328 NATURAL SCIENCE [November 
or on the upper part of the escarpment face. That the flints have 
been derived from the chalk is unquestioned, and the process by 
which they were removed from it need not be considered. During 
the first stage of the life history of the independent flints they were 
split into slabs or tablets, most of which have one flat side, and one 
showing the original external surface. Some of the flint slabs were 
flat on both sides, and they are often six or eight inches in length. 
The formation of these flint slabs was probably due to extreme cold, 
as many of the fractured surfaces resemble those of frost-flakes. 
Then a siliceous encrustation was deposited over the flint. The 
next process—leaving the chipping of the edges out of considera- 
tion for the present—was the staining of the flints to a red or 
reddish brown colour. The staining was no doubt due to the action 
of ferruginous solutions. The iron may have been derived from 
beds of iron sand in which the flints were once embedded, as grains 
of dark ferruginous sand are found still adhering to the flints in the 
hollows of chipped surfaces. Subsequently to the staining, the 
flints were scratched by some glacial agent. The striae are very 
abundant, and closely resemble those produced by ordinary glacial 
action. They were no doubt caused by the movement of pointed 
flints across the flat surfaces of other flints under considerable 
pressure. The movement of frozen masses of gravel might produce 
these scratches as well as the flow of dirt-laden ice, so that it is 
perhaps unnecessary to assume the existence of true glaciers in Kent 
on the evidence of these scratched flints alone. 
The next change in the flints was the deposition over them of a 
thin layer of silex, which covers most of the chipped surfaces, and 
often fills up the scratches. The silica occurs in two varieties, one 
brown and often very fibrous, and the other white. They may have 
been deposited at different dates. The material is a variety of 
chalcedony, sometimes having the characteristic botryoidal form of 
that mineral. 
The nature of this siliceous encrustation is not yet completely 
understood, but it must have been deposited by some siliceous 
solution similar to that which has often re-cemented shattered flints. 
There is, for example, in the Devizes Museum a flint that has 
been broken into countless fragments, many of which are as fine as 
grains of sand; but they are all united by a chalcedonic infiltration 
into a mass sufficiently solid to bear a high polish. The occurrence 
in situ of flints which have beeu similarly crushed and re-cemented 
has been recorded by Englefield and Mantell. 
One feature that renders this siliceous encrustation the more 
interesting is that it was sometimes deposited later than one set of 
glacial scratches and earlier than another set. 
The last process which the plateau flints have undergone is a 
