In Durham's dales the landscape slowly re-greens

The pub at Piercebridge has a grandfather clock that is, they say, the original of the one in the song: "The clock stopped, never to go again, when the old man died." I am willing to believe anything in the warm fug. Earlier, I had been standing in the sea-mist of Seaham Harbour, next to the bronze statue of County Durham's biggest coal-owner, Charles Stewart Vane-Tempest-Stewart, sixth Marquess of Londonderry, and wondering whether any stretch of water anywhere was quite so unwelcoming as the North Sea on a winter's day.

Seaham Harbour is a ghost town. The Vane Tempest mine, a road's width from the sea, shut down in the early 1990s.

In Belfast, in 1912, the sixth Marquess stood next to Edward Carson, Bonar Law and the Presbyterian Moderator, under the largest Union Jack ever made, as Protestants raised their hands to swear hostility to the Liberals' Irish Home Rule Bill. Buttressed by his coal revenues, the Tory grandee was endorsing the strange idea of a Loyalism that was in rebellion against the national elected government - an idea whose legacy Tony Blair, a Durham MP, has been trying to unravel.

The Londonderrys' County Durham mansion, Wynyard Hall, now belongs to Sir John Hall, who made his fortune out of the Gateshead Metrocentre shopping mall. It is as symbolic a purchase as when Ann Gloag, the co-founder of Stagecoach, bought Lord Lovat's Scottish family seat, Beaufort Castle. What is Durham's future?

At Piercebridge, two women are talking about the difficulties of opening a local advice centre. "Things get shoved through the door. Windows get broken. I wonder if you can really help them. It's an attitude." A man who lives near here had a very inventive scam. He went round the pubs on a Saturday night, after the winkle sellers had been in. He gathered up the empty shells, and sold them to befuddled drinkers in the next pubs along.

Darlington is an attractive market town. Stockton is a dump. But, in both, Geordie jauntiness means I find myself walking around with a smile on my face.

There is something American about urban Durham. Many towns were suddenly invented, for a single purpose. The Londonderrys invented Seaham Harbour in 1828. West Hartlepool was invented as a rival coal port in 1844, Consett in 1864 by the Consett Iron Company. Such towns collapsed with an American suddenness, also. The coal docks at West Hartlepool are advertised by the Teesside Development Corporation as "a marina and much more". Consett is best known for Phileas Fogg snacks.

In an earlier era of civic boosterism, this was the heartland of the corrupt architect, John Poulson, and "our friends in the north". In the dreary New Town of Newton Aycliffe - a Labour Party invention this time, but with no clear purpose - people are still trying to make liveable homes out of Poulson-designed houses.

But this is not the whole truth. Move away from the disaster areas, and you see that Durham is becoming one of the most beautiful of counties. The greening of England is happening all around you.

Defenders of the countryside often speak of it as something fixed. But it isn't a kind of glacier. More like shifting sands. In the government statisticians' latest forecasts, population will continue piling into Cambridgeshire, Dorset and Oxfordshire. These counties will get more and more suburban. In the meantime, the grass is starting to grow green on the other side of the fence.

Some counties are expected to show only tiny rises in numbers: Northumberland and Nottinghamshire, for example. And Durham, alone among English shire counties, will actually lose population. This will apply not only to the modern administrative county, but also to nearly all the towns that are historically part of Durham, from Gateshead and Sunderland in the north to Stockton and Darlington in the south.

In upland Durham, the slow re-greening began earlier and has gone further. In the dales of the Wear, Tees and Derwent, the landscape was shaped for ever by lead mining. But the trees and grass came back.

In seaward Durham, the new countryside often seems artificial. There are saplings everywhere you look. It is a literal hedging of bets. New roads have been pushed through in the hope that prosperity of the old sort may return. They are often deserted. But trees have been planted in case a pre-industrial version of Durham may work out better.

The trees are winning. Except at the Nissan plant outside Sunderland, many of the new jobs - so tenderly wooed with every sort of bribe - turn out to be low-paid, part-time, insecure.

The Penshaw monument is a replica Greek temple on a sudden hill, above a former mining village. It was built in 1844 in honour of "Radical Jack" Lambton, first Earl of Durham, and an advocate of parliamentary reform. I climb up the steep path, slippery from recent rain. At the top, I am alone inside the great Doric columns, which were meant to evoke Athenian democracy. In one direction, I see the city of Sunderland. In other directions, I stare out at sea, fields and distant hills. Nissan may not be the future after all.