The North Sea is only a recent flood in an old river valley. We must consider it not as a tract of permanent water, but as a lost hunting ground of our own ancestors, a pasturage for horses not very long ago.
A valley in Cloudland
In the year 5200 B.C. the Scandinavian glaciers, shrinking at the rate of about one mile a year (the rate of shrinkage in the Alps of St. Elias), withdrew from the province of Finland and the Baltic Lake. Let us suppose that, in that year a traveller from civilised Egypt made his way down the Rhine, and so entered the valley of North River, which is now flooded by the North Sea. At first this river wound its level way between low chalk downs, but presently the Thames came in from the West, and forested swampy clay-lands extended northward. Abreast of Aberdeen came the last chalk downs, and beyond that lay Arctic tundras where the delta widened to an ice-drifted sea nearly abreast of Faroe.
The whole valley was as varied in rock and soil as Eastern England, with little lakes, ridges of boulder clay, and downs of gorse and bracken. Northward across this verdant land crept succeeding waves of the fir, the oak, and the beech.
Out on the delta coast, far to the right, beyond a deep sea channel, rose the white Ice-cap of Sweden, whose Ice-flood filled the Norway fjords with berg-breeding glaciers. Far to the left rose the ice-clad Grampians.
The Delta people and those of the Baltic Lake were poor savages living upon shell fish, and making mounds of shell refuse round their hearths. Inland were stronger peoples who had lake villages or trenched encampments on headlands of the downs.
Cloudland horses
As the grass followed the advancing fir woods, the primitive stock of Cloudland returned to pastures from whence it had been driven by the cold. These were not Duns, Bays, or striped, but native Cloudland horses adapted to this region of little sunshine. Strong Dun was not needed to guard them from the actinic rays of sunlight, so their dull colour had yellowish, brownish and reddish tones which blended with the landscape, such colours as are worn by the Celtic ponies of Britain and other Atlantic isles.
The wild horses were evolving three utterly different types. On the chalk downs, and on the limestone tracts north of the Humber, there were lightly built, slender, graceful horses of fair height. On the clays there were horses, heavy, coarse, and slow. On the Breton, British and Scandinavian moors there were Celtic ponies.