28 MR. W. G. CLARKE ON REMAINS OF THE NEOLITHIC AGE. 
Grimes’ Graves were probably one of the largest Neolithic 
flint quarries in England. The flint is black, yet all the 
implements found on the surface in the immediate vicinity 
are weathered white or grey, resembling those from the 
South Downs and from Ringland district, and quite distinct 
from all other implements found in the neighbourhood. Not 
only are these implements grey or white, but by far the 
greater proportion of those found in the district are shades 
of grey, blue, or yellow. For statistical purposes I selected 
those implements which appear to be perfect in form in my 
collection from Thetford district. Of these there are 593. 
and only 54 can be described as black, and very few indeed 
are of that perfect black which is characteristic of excavated 
flint from the immediate neighbourhood. Various shades 
of grey (including a large number of implements which may 
quite conceivably originally have been black) numbered 287 ; 
various shades of yellow, 130 ; various shades of blue, 87 ; 
and miscellaneous colours, 35. Yet strata of grey, yellow, 
or blue flint do not occur in the neighbourhood. Either the 
implements are made of isolated pebbles, or the colour of 
excavated flint from the chalk has been altered by atmospheric 
changes. That a certain proportion are made from pebbles 
is probable, for out of 593, 279 have still some portion of the 
original crust remaining. Another possibility is that members 
of the Neolithic tribe which worked Grimes’ Graves, did not 
themselves value the black flint very highly, and exchanged 
it for flint of other colours from other districts. Against 
the theory of barter must be placed the undoubted fact that 
near the flint workings at Grimes’ Graves the implements are 
as a general rule larger in size than is the case elsewhere in 
the district. Generally speaking, also, there is a tendency * 
for implements to get smaller in proportion as one gets further 
away from Grimes’ Graves, those on Thetford Warren and 
Thetford Abbey Heath being almost invariably small. 
Exceptions, however, occur not infrequently. Then, again, 
the knappers find by experience that the more delicate 
chipping can only be done when flint is newly quarried. As 
to the delicacy of the workmanship of local implements 
