I find it difficult to imagine Britain covered by ice 1,000ft thick. But that is what one had to bear in mind to get the best out of a remarkable meeting on Wednesday in Delamere Forest, a few miles from Chester.
When the glaciers retreated northwards at the end of the last ice age, colossal lumps broke off them and forced down the sub-strata into hollows now known as kettle-holes. Delamere contains several, and this week attention was focused on the largest, Blakemere Moss, nearly a mile long and up to half a mile wide.
Final settlement of the earth's surface left this oblong hollow without any exit for the water that trickled in off surrounding land. The result was a peat bog, and for hundreds of years man struggled to drain it so that it would grow trees.
Local legend has it that in about 1815, prisoners from the Napoleonic wars were set to dig drainage ditches and, in particular, one exit channel. Foresters then planted the moss with oak, and, when this failed, with Scots pine. In the Twenties the area was taken over by the Forestry Commission, which in the Forties tried yet again with a mixture of pine and western hemlock.
This, too, grew poorly, and over the years fortunes were spent on keeping the ditches open. Then in 1992 the commission took a momentous decision: to scrap the scruffy trees and see if it could return the area to bog, or even create a lake. As one senior officer remarked, "For people whose lives are dedicated to growing trees, it was such a conceptual leap that for a long time nobody could face it."
The commission established that there would be no local opposition to the idea, and last June a harvester machine went to work; 16 weeks later, 4,500 tons of timber had been cleared, leaving a sea of lop and top. A contractor was called in to pile it into heaps, which will be burnt as soon as they are dry enough.
Having created a spectacular opening in the forest, the commission now has to decide what to do with it. A concrete sluice has been built on the one exit drain, and it will be possible to raise the water level by simply putting in boards across the 5ft opening. But should the entire area be flooded? What will happen, in biological and hydrological terms, if 100 acres go under water?
Hence Wednesday's meeting, at which a dozen scientists were invited to give their views. A visit to the site made a profound impression. Suddenly, in the middle of the forest, we came on this vast open area, dotted with hundreds of brushwood heaps, and surrounded by a curving fringe of Scots pines, which, standing on higher, sandy ground, have grown tall and straight.
The Napoleonic drainage ditches were coated with ice. Between them the peat quaked beneath our feet. Maybe it was because I had bought a postcard of a pterodactyl in the visitor centre, but I felt I had stumbled into Conan Doyle's lost world. When a peat specialist rammed his sampling tube straight down, and came up with a dark brown core a metre long, it was eerie to think that the earth-like substance at the bottom had not seen the light of day for at least 5,000 years.
The scientists made numerous suggestions. One was that the incoming water be analysed to find out what plants a bog might support; another, that pits should be dug before flooding starts, so the moss will eventually encompass several ponds.
One major worry is that millions of dead hemlock leaves may poison the outflow; another possibility is that the water may not rise high enough to prevent the birch, a notorious survivor, from regenerating. Two things are certain: that Blakemere Moss will become a valuable new wetland; and that specialists will follow with the utmost fascination the steps taken to create it.
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