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And how long ago were those days of mammoths and reindeer, lions and hyaenas? We must talk not of days, but of ages; we know nothing of days or years. As the late lamented Professor Sedgwick has well said:-

‘We allow that the great European oscillation, which ended in the production of the drift (the boulder clay, or till), was effected during a time of vast, but unknown length. And if we limit our inquiries, and ask what was the interval of time between the newest bed of gravel near Cambridge, and the oldest bed of bogland or silt in Cambridgeshire and Norfolk, we are utterly at a loss for a definite answer. The interval of time may have been very great. But we have no scale on which to measure it.’

Let us suppose, then, the era of ‘gravels’ past; the valleys which open into the fen sawn out by rivers to about their present depth. What was the special cause of the fen itself? why did not the great lowland become a fertile ‘carse’ of firm alluvial soil, like that of Stirling?

One reason is, that the carse of Stirling has been upheaved some twenty feet, and thereby more or less drained, since the time of the Romans. A fact patent and provable from Cramond (the old Roman port of Alaterna) up to Blair Drummond above Stirling, where whales’ skeletons, and bone tools by them, have been found in loam and peat, twenty feet above high-water mark. The alluvium of the fens, on the other hand, has very probably suffered a slight depression.

But the main reason is, that the silt brought down by the fen rivers cannot, like that of the Forth and its neighbouring streams, get safe away to sea. From Flamborough Head, in Yorkshire, all down the Lincolnshire coast, the land is falling, falling for ever into the waves; and swept southward by tide and current, the debris turns into the Wash between Lincolnshire and Norfolk, there to repose, as in a quiet haven.

Hence that vast labyrinth of banks between Lynn and Wisbeach, of mud inside, brought down by the fen rivers; but outside (contrary to the usual rule) of shifting sand, which has come inward from the sea, and prevents the mud’s escape–banks parted by narrow gullies, the delight of the gunner with his punt, haunted by million wild-fowl in winter, and in summer hazy steaming flats, beyond which the trees of Lincolnshire loom up, raised by refraction far above the horizon, while the masts and sails of distant vessels quiver, fantastically distorted and lengthened, sometimes even inverted, by a refraction like that which plays such tricks with ships and coasts in the Arctic seas. Along the top of the mud banks lounge the long black rows of seals, undistinguishable from their reflection in the still water below; distorted too, and magnified to the size of elephants. Long lines of sea-pies wing their way along at regular tide-hours, from or to the ocean. Now and then a skein of geese paddle hastily out of sight round a mud-cape; or a brown robber gull (generally Richardson’s Skua) raises a tumult of screams, by making a raid upon a party of honest white gulls, to frighten them into vomiting up their prey for his benefit; or a single cormorant flaps along, close to the water, towards his fishing ground. Even the fish are shy of haunting a bottom which shifts with every storm; and innumerable shrimps are almost the only product of the shallow barren sea: beside, all is silence and desolation, as of a world waiting to be made.

So strong is the barrier which these sea-borne sands oppose to the river-borne ooze, that as soon as a seabank is built–as the projectors of the ‘Victoria County’ have built them–across any part of the estuary, the mud caught by it soon ‘warps’ the space within into firm and rich dry land. But that same barrier, ere the fen was drained, backed up for ages not only the silt, but the very water of the fens; and spread it inland into a labyrinth of shifting streams, shallow meres, and vast peat bogs, on those impervious clays which floor the fen. Each river contributed to the formation of those bogs and meres, instead of draining them away; repeating on a huge scale the process which may be seen in many a highland strath, where the ground at the edge of the stream is firm and high; the meadows near the hillfoot, a few hundred yards away, bogland lower than the bank of the stream. For each flood deposits its silt upon the immediate bank of the river, raising it year by year; till–as in the case of the ‘Levee’ of the Mississippi, and probably of every one of the old fen rivers–the stream runs at last between two natural dykes, at a level considerably higher than that of the now swamped and undrainable lands right and left of it.