42 Mr. Henry Walker's Lecture:
patchy ; and at length it disappears where the slope of the
valley begins, and here we meet the records of a later period
—records which did not begin until after this great sheet
of ice had disappeared in our south-eastern area of Britain.
The memorials of glacial Essex of which we thus get a
glimpse on the hill-tops and plateaux take us back to
the climate and time of the northern group of the Ilford
fossil mammalia. We have got back to the age of the
mammoth and woolly rhinoceros. It was a long enduring
age in Britain, and marked by many eventful and complex
phenomena. But we need only look at the later stage of
this incalculably long period, and witness, as it were, the
incoming of the more varied fauna with which we find
these northern animals associated in the fluviatile graves
of the Roding Valley.
BEGINNINGS OF PLEISTOCENE ESSEX.
At the time when the ice thus prevailed, the land—
except the summits of the most elevated districts, as the
Knockholt Downs, which as we look south from the Essex
heights appear projected on the sky-line—was for an untold
period of time lost to view beneath the sea. It suffered
the slow but sure spoliation and destruction of all vegetable
and animal life by that wonderful vicissitude the Great
Marine Submergence. Gradually sinking beneath the
waters, this part of the land-surface of Pliocene Britain,
with its forests and pastures, and all the varied animal life
of the period, its river courses and all terrestrial features,
became a sea-floor. Here in this submarine condition it
was overlaid as the slow years went on with the sediment
and drifting waste of the sea, with the dropping debris
transported from land still above the waters, and with its
own looser rocks drifted to lower levels.
As the land sank, and again as it emerged, pebble-beds
and gravels we see around us to-day were disturbed
and spread over wider areas, gathered in the submarine
valleys, and mingled with the mud and sand. The former
hills and plains of heath-clad Essex were wasted and