44 Mr. Henry Walker's Lecture:
of Europe that a more varied flora and fauna could advance.
But that time had not yet arrived. The humbler but not
insignificant herbaceous plants were the prevailing vege-
tation, and then began to flourish the reindeer moss, the
branching "Cladonia" which has ever since lived on our
heaths and commons, reminding us to-day of the British
reindeer that in time found its way to the glacial Essex
hills.
THE GREAT EUROPASIAN INVASION.
And the time of more habitable conditions did arrive.
Gradually the rising land was more and more uncovered
by the retreating sea and the northward-shrinking glaciers.
Reversions to the old Arctic weather still came on in the
winters, but in the summers a giant herbaceous vegetation
like that of Siberia established itself. Tall Umbellifers,
almost rivalling trees in stature during their short
life, and coarse but vigorous grasses made an herbaceous
forest and feeding ground for the future incoming herds.
The land continued to rise: the German Ocean, from
which the waters had now retreated northwards to the
outlying depths, became a land-valley, and the westward
and northward-travelling herbs and shrubs and forest
trees gradually took possession. Southward, the valley
of the English Channel had been similarly transformed,
clothed with forests and open pastures, varied with mountain
and ravine, and perhaps chains of lakes. Far on to the
coast of Africa, where no Straits of Gibraltar then inter-
vened, the land was continuous from Britain. Favouring
climatal conditions were all that was wanted for the animals
of the north and south alternately to visit and. occupy
each other's land. The rivers of the now united countries
watered a common land, those of the British area becoming
confluent with those of the continent; the fresh-water
denizens of the one were no longer shut off by the sea from
inhabiting each other's waters.
By this union of England with the Continent, the great
physical barrier to the rehabilitation of the long-lost and
long-barren land was now removed. Alternations of climate,