94
THE ESSEX NATURALIST.
of an underground surface of chalk, soil-creep, the drag of ice,
or the like, which are fully adequate in themselves.
In the boulder clays, or other glacial deposits, one can scarcely
expect to find the direct proof of the flaking process, with the
flakes still fitting against the parent block. But I have found such
proof in situ in Chalk that has been disturbed by the drag of ice.
A factor of some importance that is clearly revealed by-
experiment is that the friction occasioned by the edge of the
flint passing across the rough surface of another stone greatly
facilitates the flaking process.
A still more important fact to be learnt from experiment is
the influence of the form of the flint as mainly determining its
flaking properties under mechanical force. It is not merely
experiment upon any piece of flint, but it is the shape of the piece
that matters supremely. A piece split off an original nodule
possesses one approximately flat surface fractured through the
body of the nodule, with a higher or lower rounded back formed
by the outer cortex. More often than not the edges around most,
if not the whole, of its circumference are acute ; in a word,
it is of plano-convex form, varying in detail in its size and
proportions. This is the key form in the understanding of
natural flaking. Whether it be under fortuitous flaking by
cart-wheels or in wash-mills, under carefully planned mechanical
experiment, or from the direct observation of flaking by natural
agencies, the plano-convex form gives flaking results that are
selective and systematic to a degree that is little short of amazing.
This selective effect takes the form of parallel flaking along
the edges, starting regularly from the flat surface, and running
up the sides, and no one could deny that it carries a deceptive
resemblance to the work of intelligent design. It would appear
a reasonable supposition that unguided force acting indis-
criminately from all directions would result in equally
indiscriminate flaking, but this is contrary to fact. A marked
tendency towards the limitation of the flaking to these particular
selective directions is good evidence in favour of the operation
of indiscriminate force : it is most emphatically not evidence
in favour of human work, as it is erroneously supposed to be.
Human flaking, even of the simplest and most primitive
character, is independent of these mechanical limitations.