A fairly demanding but spectacular walk through Northumberland's geological history.
Distance 4.5 miles (7.2km)
Minimum time 3hrs
Ascent/gradient 590ft (180m)
Level of difficulty Hard
Paths Mostly hill footpaths, 8 stiles
Landscape Hills and river gorge
Suggested map aqua3 OS Explorer OL16 The Cheviot Hills
Start/finish NT 919063
Dog friendliness Keep on lead on road and near sheep on hills
Parking Car park at Alwinton
Public toilets At car park
Notes Close to MOD artillery range over Barrow Scar. When red flags flying, walk may be inadvisable. Contact Range Control Officer on 01830 520569 or 0191 239 4261
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1 Turn right, out of the car park and follow the road for 700yds (640m) to a gate on the left leading to Barrow Mill. Go through the gate and down to the farm, passing the remains of a corn-drying kiln that dates from 1812. Go through another gate into a field, cross this and go through a gate to the river bank. Ford the river. After a period of rain, this will involve getting your feet wet.
2 Enter the field and follow the fence to the right to a gate. Go through this or over the stile about 20yds (18m) away to the left and continue to the derelict farm buildings. Follow the track up the hillside to the right-hand corner of the conifer forest.
3 About 50yds (46m) before reaching a signpost marking the edge of a military firing range, follow a less well-defined track across the heather-covered hillside to the right, rising slightly, until you come to a wire fence. Follow this over the top of Barrow Scar, keeping the fence on your right. When you meet a second fence, follow this to a stile. Cross the stile and go down to an obvious loop in the river. In late summer, the bracken here may be deep and the track obscured.
4 At the river bend, cross a stile, then another after a further 100yds (91m). Cross over the field and a stile into the farmyard at Linshiels. Go through the farmyard, across two bridges and join the road. Turn left and follow the road until just past the farm buildings, to a signpost pointing to Shillmoor.
5 Go up the hillside, over a stile and follow the track overlooking the gorge and its waterfalls. This is the most spectacular part of the walk. For a short distance, the slopes below are quite precipitous and care is needed, though the track is good. When the track splits, keep to the higher branch and go round the hillside to join a more prominent track leading up from the left. Turn right and follow this track uphill.
6 At the top of the slope continue across level ground, then descend to a stile. Cross this and follow the track, over another stile and down to the road. Follow the road for 1 mile (1.6km) back to Alwinton.
The oldest rocks in Northumberland, older even than the Alps, are those of the Cheviot Hills. They were formed by volcanic activity, which began about 380 million years ago, and once rose to heights in excess of 15,000ft (4,572m). Relentless weathering has worn down the mountains and rounded their summits, so that Cheviot itself, the highest peak, is now only 2,677ft (816m) high. The heat and pressure of further eruptions sometimes cooked and hardened the earlier rocks, so that they became more resistant to erosion and now stand as craggy tors above the Breamish and Harthope valleys.
Shallow seas then washed the feet of the mountains and aided their erosion. Deposits of mud and sand were laid down and compacted into shales and sandstones. The living creatures of these seas extracted calcium salts from the water to form their shells and bones, which then added to the sediments as chalk and limestone. The successive layers of sedimentary rock are known as the cementstones and are around 340 million years old.
After the the formation of the cementstones, the whole area became the delta of a vast river that flowed out of a North Atlantic landmass. The coarse-grained sands from this formed a layer 500-1,000ft (152-305m) thick. This became the fell sandstones that cover much of central Northumberland. Emperor Hadrian used these hard rocks to build his wall. Later, men like John Dobson, used them to construct many of Newcastle's buildings, of which the Central Railway Station is a good example.
The most recent period of geological activity, beginning about one million years ago, has been characterised by the ice ages, during which ice sheets covered Northumberland's hills, to a height of 2,000ft (610m). Glaciers, several hundred feet thick carved broad U-shaped valleys in the hills. After their retreat came the rivers, which continue their erosion to the present day, seaming the hillsides with narrow, V-shaped valleys that have slowly exposed the rocks of the different geological eras.
Nowhere is Northumberland's geological history better laid out to view than around the gorge of the River Coquet, west of the village of Alwinton. To the north are the volcanic Cheviot Hills, while to the south are the fell sandstones. And in the gorge itself, at Barrow Scar, the layers of the cementstones lie fully exposed.
At Harbottle are the remains of a castle built in the reign of Henry II as defence against the Scots. Lady's Well, at Holystone, was built by the Romans around a spring that was used for early Christian baptisms. Bishop Paulinus is said to have baptised 2,000 people here on Easter Sunday, ad 627.
The Rose and Thistle, Alwinton, is a good pub, but does not serve meals. Sandwiches and side salad are served at the Star, Harbottle, at lunch times only. Try the bar meals at the Three Wheat Heads or at the Cross Keys, Thropton, 8 miles (12.9km) from Alwinton.
The first half of the walk is over fell sandstone, the second over volcanic rock. As well as rock textures, note the different vegetation: grassy and bracken-covered on the volcanic slopes, heathery on the more acidic fell sandstones. The layered structure of the cementstones at Barrow Scar is well observed from the second part of the walk.