The Lake is also divided into two unequal portions by the straits of White Horse, where vessels are often weather-bound, and cannot make way against the wind, which sets a current through the narrow channel.  There is no tide; the sweet waters do not ebb and flow; but while I thus discourse, I have forgotten to state how they came to fill the middle of the country.  Now, the philosopher Silvester, and those who seek after marvels, say that the passage of the dark body through space caused an immense volume of fresh water to fall in the shape of rain, and also that the growth of the forests distilled rain from the clouds.  Let us leave these speculations to dreamers, and recount what is known to be.

For there is no tradition among the common people, who are extremely tenacious of such things, of any great rainfall, nor is there any mention of floods in the ancient manuscripts, nor is there any larger fall of rain now than was formerly the case.  But the Lake itself tells us how it was formed, or as nearly as we shall ever know, and these facts were established by the expeditions lately sent out.

At the eastern extremity the Lake narrows, and finally is lost in the vast marshes which cover the site of the ancient London.  Through these, no doubt, in the days of the old world there flowed the river Thames.  By changes of the sea level and the sand that was brought up there must have grown great banks, which obstructed the stream.  I have formerly mentioned the vast quantities of timber, the wreckage of towns and bridges which was carried down by the various rivers, and by none more so than by the Thames.  These added to the accumulation, which increased the faster because the foundations of the ancient bridges held it like piles driven in for the purpose.  And before this the river had become partially choked from the cloacae of the ancient city which poured into it through enormous subterranean aqueducts and drains.

After a time all these shallows and banks became well matted together by the growth of weeds, of willows, and flags, while the tide, ebbing lower at each drawing back, left still more mud and sand.  Now it is believed that when this had gone on for a time, the waters of the river, unable to find a channel, began to overflow up into the deserted streets, and especially to fill the underground passages and drains, of which the number and extent was beyond all the power of words to describe.  These, by the force of the water, were burst up, and the houses fell in.

For this marvellous city, of which such legends are related, was after all only of brick, and when the ivy grew over and trees and shrubs sprang up, and, lastly, the waters underneath burst in, this huge metropolis was soon overthrown.  At this day all those parts which were built upon low ground are marshes and swamps.  Those houses that were upon high ground were, of course, like the other towns, ransacked of all they contained by the remnant that was left; the iron, too, was extracted.  Trees growing up by them in time cracked the walls, and they fell in.  Trees and bushes covered them; ivy and nettles concealed the crumbling masses of brick.