1897] THE AUTHENTICITY OF PLATEAU MAN — 329 
certain amount of polishing by the action of blown sands. Some- 
times the whole surface of the flint has been thus polished, but 
specimens often occur in which the action has been limited to one 
side. Many of the flints of the Thames gravels, as, for example, at 
Clapham, show the same feature. In the cases of these low level 
gravels, the polishing was probably effected at a time of drought, 
when the pebbles were exposed and the river sand was dry and loose. 
We therefore see that these plateau flints have been subjected 
to six different processes, all of which are undoubtedly natural, and 
each of which has left clearly recognisable traces. Taken in order 
of date, the processes are :—1st, splitting of the original flints into 
slabs, probably by frost; 2nd, a deposition of a siliceous encrusta- 
tion; 3rd, iron staining; 4th, scratching by some glacial agent ; 
5th, deposition of a second siliceous encrustation ; 6th, polishing by 
blown sand, ; 
This series forms a chronological table by which we can 
determine the relative dates of the various chippings of the flints 
which are affirmed to be the work of man. I think it is quite clear 
from the evidence of the flints that natural agencies are sufficient to 
account for every splinter and scratch that they exhibit. 
The first fact that tells against the artificial chipping of the 
flints is that the chipping is of very different dates. The process 
must have been continued for a considerable length of time. It is 
-not difficult to distinguish between the chippings of different periods. 
The earliest fractures are the largest, as might be expected, since the 
conditions were the most rigorous. As the climate became milder 
the forces that acted on the flints became feebler, and the chips 
removed were therefore smaller. On some specimens it is possible 
to detect chippings of three different periods. The first set were 
struck off before the flints were coloured red ; the second set broke 
across the margins of the first, and sometimes exposed part of the 
uncoloured flint below. Then came an interval during which the 
glacial scratches were made. These scratches cut across the surfaces 
formed by the first two sets of chippings. The fractures of the third 
set, on the other hand, are never scratched, but have themselves cut 
across the striae. These latest chips were small, and usually more 
distinctly conchoidal than the others, and in many instances they 
present the appearance of small frost-flakes. 
As definite illustrations of the different dates of the chippings, 
let us examine in detail four flints which were given to me by Mr 
Harrison as fairly good implements (Plate IX.). 
The first is shewn in Fig. 1 of the Plate It was found by Mr 
Harrison at South Ash, and is numbered 4997. Its size is 6 cm. 
1 For the photographs I must express my indebtedness to Mr T. H. Powell of 
Denmark Hill. 
