THE FOUNDATIONS OF PREHISTORY. 95
The tabular form of flint is the second in importance in
flaking by mechanical force. This introduces the modification
that the one-way selective flaking of the plano-convex is changed
to two-way flaking, one from either of the two flat faces of the
tabular flint. Apart from the differences that inevitably arise
from that modification, the general results from the plano-
convex and the tabular forms may be taken together. Both
alike are chipped along the edges into hollow notches, double-
notches-with-point (or bow-scrapers), rostro-carinates, straight
edges, angles, ogees, and complex curves in great variety.
That is to say, the whole gamut of the eolithic types.
The reason for the automatic selectivity of flaking that has
been described above, which to a superficial view might appear
incredible, is in reality quite simple. It arises from the fact that
flaking in those directions requires a very much smaller force
than flaking in all other directions. In consequence of this
selectivity is the greatest when the force is the minimum
necessary to do the work. Conversely, the greater the force
the more casual flaking is produced in accidental, or non-selective,
directions.
This explains why selective flaking is dominant in the super-
ficial soil-creep drifts, and casual flaking in geological formations
such as the Triassic pebble beds which have been under the
pressure of a heavy load of superincumbent strata. Even in
the latter formation selective results are not infrequent, arid
eolithic forms that are perfectly true to type are made out of
split pebbles of Bunter quartzite.
I originally described this selective flaking under the name
of "the principle of the planes of least resistance," but while
I feel that the present fashion for finding better names for things
is rather overdone, I think that in this case the alteration should
be made. The cause of the selectivity lies in the form of the
piece of flint, and the angles of its edges, rather than in its
structure as suggested or implied by the original name.
The clearest and most direct method of obtaining an insight
into this selective flaking is to drop a pebble of tough quartzite
from a height of a few feet upon a flint of plano-convex form
placed on the ground. By turning the flint about, blows of
uniform force and velocity can be directed upon it from different