Winter’s first sustained frost still hasn’t thawed even though it is after noon, so we head up the valley to Allenheads. There the land is bright under a clear sky and it’s six degrees warmer. The walk up to Killhope Law begins where a lead smelt mill stood above the East Allen river. Green mounds hint at the archaeology and the short grass of spoil heaps is clipped tight by sheep and rabbits. A long, low bulge like an ancient earthwork runs uphill for about two miles, a 19th-century flue that carried fumes to a long-gone chimney. We are following the Carrier’s Way, a packhorse route that brought lead ore from one valley to the other, from Weardale over the tops to the smelt mill. To either side, abandoned houses, their sandstone roofs collapsed inwards, are sheltered by beech and sycamore. I try to interpret the sumps and tumps in a landscape pocked with small quarries and heathery hillocks where grouse stand alert. They cluck in alarm, silhouetted by the low afternoon sun. A rounded cairn on Killhope Law pulls us on up the straight march of the track. Looking back, the flat waters of Dodd Reservoir reflect a sharp blue sky, while far beyond, the Tyne Valley holds a thick rope of fog that creeps up its side valleys. After an hour, the way levels out along the watershed. Even up here there are signs of workings and lumps of galena shine purple among the rocks. The blanketing heather is broken by deep peat hags and shards of ice on puddles. In an old quarry, a rough stone hut, sheep-trod inside, fading graffiti is inscribed in its mottled render. Killhope Law is topped by a disintegrating trig point and the stump of a post, once a 30ft-high flagpole. The 360-degree view is spectacular. We are almost at the meeting point of three counties and can see Skiddaw and Blencathra to the west in Cumbria, and Weardale in Durham to the south, while we stand just inside Northumberland. Invigorated, we head back down as fog edges up the valley.