The great river Severn coming down from the north, with England on one bank and Wales upon the other, entered the sea, widening out as it did so.

Just before it reached the sea, another lesser river, called the Avon, the upper part of which is still there, joined it passing through this cleft in the rocks.
But when the days of the old world ended in the twilight of the ancients, as the salt ocean fell back and its level became lower, vast sandbanks were disclosed, which presently extended across the most part of the Severn river.

Others, indeed, think that the salt ocean did not sink, but that the land instead was lifted higher.

Then they say that the waves threw up an immense quantity of shingle and sand, and that thus these banks were formed.

All that we know with certainty, however, is, that across the estuary of the Severn there rose a broad barrier of beach, which grew wider with the years, and still increases westwards.
It is as if the ocean churned up its floor and cast it forth upon the strand.
Now when the Severn was thus stayed yet more effectually than the Thames, in the first place it also flowed backwards as it were, till its overflow mingled with the reflux of the Thames.