THE ESSEX NATURALIST.
live side by side, and also the sweeping changes which take
place in the frontiers between different races as the centuries
roll by, even without taking into account the pressure of
European colonists.
In like manner, we now view Palaeolithic problems from
a new perspective, namely, that of different races in some part
contemporary one with another, living in adjoining areas.
For example, one formerly thought that the Mousterian
gradually changed by process of evolution into the Aurignacian.
We now know that was not so; but that the relation of the
Aurignacian to the Mousterian was like that of the English to
the Australian native. On certain French cave sites it is sig-
nificant that after the Mousterian had given place to the Aurig-
nacian, the fluctuating fortunes of tribal warfare brought the
Mousterians back again to live a second time in the home of
which they had been dispossessed—only to be a second time,
and finally, driven out by the Aurignacians.
Or again, we formerly placed the Aurignacian, Solutrian,
and Magdalenian in simple sequence. It now appears to be
established that the Solutrians never at any time occupied the
whole of Western Europe, but that they were invaders who
occupied a considerable area during Later Aurignacian or
Earlier Magdalenian times. In short, that the Solutrian period
must be ruled out of the general time-scale. But I think we
do find, as one might expect, evidence of the culture of one race
influencing that of another.
These considerations, if sound, as I believe them to be, pro-
foundly modify the attitude we should take up in approaching
our local problems.
Theoretical Succession of the River Terraces.
It is familiar knowledge that as a river excavates its valley
it leaves a succession of terraces of river deposits on the side slopes
of the valleys from above downwards. This, again, though
broadly true, is subject to more irregularities and complexities
than is generally realised. At the present day the water-level of
a continental river may rise as much as fifty feet vertically above
the normal during a big flood ; while below the normal water-
level of the river there is the depth of water to the unseen river-
bed below. These occasional big floods may leave behind them