50 Mr. Henry Walker's Lecture:
land-surface arose above the icy waters, and began to be
sculptured into water-sheds and river-basins, down to
these latest days, such valleys have served as great hiding-
places and storehouses for the varied drift of the landscapes
which drain into them.
From the deposits of our old rivers we learn the kind
of denizens which dwelt on the adjacent snow-clad hills
and plains, or among the forests, jungles, swamps, and
prairies of mammoth-haunted England. During long and
eventful ages, marked by great changes in the climate,
zoology, and physical geography of our land, the rivers
have entombed and treasured up the drift of the wide
terrestrial area around them. They have thus preserved,
until future ages, many a relic which would have been
left to decay or sudden destruction on the land, had it not
been swept by floods to the care and custody of the valley.
In this way the rivers were acting as the chroniclers of
physical England long ere human historians appeared. In
ages long antecedent to the annals of man, the Thames
was storing its valley with that wondrous archaeology of
Nature which we to-day in weekly rambles are privileged
to explore. Through an incalculable long period, marked
by changes in the climate and the separation of Britain
from the Continent and by the dying out or dispersal of
old-world forms of life, the Thames and its tributaries,
from the Cotswolds downwards, have been pouring their
waters down to the great receiving-drain of the lower
Thames Valley. And so to-day we learn from these invo-
luntary chroniclers what strange inhabitants dwelt in this
Essex country of ours, fellow-denizens with man, and yet
of whom man himself has left no record.
These river graves at Ilford and Grays Thurrock are to
the Londoner what the limestone caves of Victoria, Kirk-
dale, and Torquay are to the inhabitants of Yorkshire and
Devonshire. They are a natural museum of the mammoth
and rhinoceros period in England. In the valley of the
lower Thames, the rocks are not of the limestone texture
which elsewhere has been gradually hollowed out into
caverns and fissures to serve as sepulchres for our old