There exhales from this oozy mass so fatal a vapour that no animal can endure it. The black water bears a greenish-brown floating scum, which for ever bubbles up from the putrid mud of the bottom. When the wind collects the miasma, and, as it were, presses it together, it becomes visible as a low cloud which hangs over the place. The cloud does not advance beyond the limit of the marsh, seeming to stay there by some constant attraction; and well it is for us that it does not, since at such times when the vapour is thickest, the very wildfowl leave the reeds, and fly from the poison. There are no fishes, neither can eels exist in the mud, nor even newts. It is dead.
The flags and reeds are coated with slime and noisome to the touch; there is one place where even these do not grow, and where there is nothing but an oily liquid, green and rank. It is plain there are no fishes in the water, for herons do not go thither, nor the kingfishers, not one of which approaches the spot. They say the sun is sometimes hidden by the vapour when it is thickest, but I do not see how any can tell this, since they could not enter the cloud, as to breathe it when collected by the wind is immediately fatal. For all the rottenness of a thousand years and of many hundred millions of human beings is there festering under the stagnant water, which has sunk down into and penetrated the earth, and floated up to the surface the contents of the buried cloacæ.
Many scores of men have, I fear, perished in the attempt to enter this fearful place, carried on by their desire of gain. For it can scarcely be disputed that untold treasures lie hidden therein, but guarded by terrors greater than fiery serpents. These have usually made their endeavours to enter in severe and continued frost, or in the height of a drought. Frost diminishes the power of the vapour, and the marshes can then, too, be partially traversed, for there is no channel for a boat. But the moment anything be moved, whether it be a bush, or a willow, even a flag, if the ice be broken, the pestilence rises yet stronger. Besides which, there are portions which never freeze, and which may be approached unawares, or a turn of the wind may drift the gas towards the explorer.
In the midst of summer, after long heat, the vapour rises, and is in a degree dissipated into the sky, and then by following devious ways an entrance may be effected, but always at the cost of illness. If the explorer be unable to quit the spot before night, whether in summer or winter, his death is certain. In the earlier times some bold and adventurous men did indeed succeed in getting a few jewels, but since then the marsh has become more dangerous, and its pestilent character, indeed, increases year by year, as the stagnant water penetrates deeper. So that now for very many years no such attempts have been made.
The extent of these foul swamps is not known with certainty, but it is generally believed that they are, at the widest, twenty miles across, and that they reach in a winding line for nearly forty. But the outside parts are much less fatal; it is only the interior which is avoided.
Towards the Lake the sand thrown up by the waves has long since formed a partial barrier between the sweet water and the stagnant, rising up to within a few feet of the surface. This barrier is overgrown with flags and reeds, where it is shallow. Here it is possible to sail along the sweet water within an arrow-shot of the swamp. Nor, indeed, would the stagnant mingle with the sweet, as is evident at other parts of the swamp, where streams flow side by side with the dark or reddish water; and there are pools, upon one side of which the deer drink, while the other is not frequented even by rats.
The common people aver that demons reside in these swamps; and, indeed, at night fiery shapes are seen, which, to the ignorant, are sufficient confirmation of such tales. The vapour, where it is most dense, takes fire, like the blue flame of spirits, and these flaming clouds float to and fro, and yet do not burn the reeds. The superstitious trace in them the forms of demons and winged fiery serpents, and say that white spectres haunt the margin of the marsh after dusk. In a lesser degree, the same thing has taken place with other ancient cities. It is true that there are not always swamps, but the sites are uninhabitable because of the emanations from the ruins. Therefore they are avoided. Even the spot where a single house has been known to have existed, is avoided by the hunters in the woods.
They say when they are stricken with ague or fever, that they must have unwittingly slept on the site of an ancient habitation. Nor can the ground be cultivated near the ancient towns, because it causes fever; and thus it is that, as I have already stated, the present places of the same name are often miles distant from the former locality. No sooner does the plough or the spade turn up an ancient site than those who work there are attacked with illness. And thus the cities of the old world, and their houses and habitations, are deserted and lost in the forest. If the hunters, about to pitch their camp for the night, should stumble on so much as a crumbling brick or a fragment of hewn stone, they at once remove at least a bowshot away.
The eastward flow of the Thames being at first checked, and finally almost or quite stopped by the formation of these banks, the water turned backwards as it were, and began to cover hitherto dry land. And this, with the other lesser rivers and brooks that no longer had any ultimate outlet, accounts for the Lake, so far as this side of the country is concerned.
At the western extremity the waters also contract between the steep cliffs called the Red Rocks, near to which once existed the city of Bristol. Now the Welsh say, and the tradition of those who dwell in that part of the country bears them out, that in the time of the old world the River Severn flowed past the same spot, but not between these cliffs. 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. Thus the inland sea of fresh water was formed; though Silvester hints (what is most improbable) that the level of the land sank and formed a basin. After a time, when the waters had risen high enough, since all water must have an outlet somewhere, the Lake, passing over the green country behind the Red Rocks, came pouring through the channel of the Avon.
Then, farther down, it rose over the banks which were lowest there, and thus found its way over a dam into the sea. Now when the tide of the ocean is at its ebb, the waters of the Lake rush over these banks with so furious a current that no vessel can either go down or come up. If they attempted to go down, they would be swamped by the meeting of the waves; if they attempted to come up, the strongest gale that blows could not force them against the stream. As the tide gradually returns, however, the level of the ocean rises to the level of the Lake, the outward flow of water ceases, and there is even a partial inward flow of the tide which, at its highest, reaches to the Red Rocks. At this state of the tide, which happens twice in a day and night, vessels can enter or go forth.