Achmelvich

Ascent — around 100 metres

Difficulty — easy on a good path, optional rocky coastal exploration

Duration — 2 hours there and back

Start — grid reference [NC 057 247]

The walk starts at Achmelvich and follows a good path across the Lewisian Gneiss to the old meal mill at Alltanabradhan. This is a good family outing for all ages, but note that the optional return along the cliffs requires good footwear and should only be undertaken by experienced walkers. Others can return by the outward route.

The car park at Achmelvich has public toilets and a ranger’s hut, which is full of useful information about the flora and fauna of the area. From the car park follow the track signposted to Alltanabradhan. The track skirts an area of ‘machair’, grassland formed on blown sand made up from tiny shell fragments. Because these crushed shells are rich in calcium carbonate, the machair supports a rich variety of wild flowers. Machair is almost entirely confined to the Northwest Highlands and Islands, because the Lewisian Gneiss that forms the coastline in this area is very hard and does not erode easily, so that the shell sand does not become diluted with ordinary beach sand.

As you walk along the track, there is a steep cliff on your right. Where the track turns to the left, climb up a short grassy slope to look at outcrops directly in front of you [1] [NC 05877 25009]. This is typical Lewisian Gneiss, with pink and grey bands contorted into swirly patterns. The pink bands are made up mainly of two minerals, translucent grey quartz and pink to white feldspar. The darker bands are composed largely of dark green crystals of amphibole that sparkle in the sun. These rocks originally formed nearly 3000 million years ago and were then metamorphosed at high temperatures and pressures, up to 25 kilometres beneath the Earth’s surface.

After a further hundred metres or so, the track crosses a small rise and turns sharply right. Just before the turn, in a rock cutting on the right-hand side of the track is a steep band of much darker rock, about 1.5 metres wide. This dark band is a Scourie Dyke, formed from magma that forced its way through the older gneiss and then cooled and solidified to form a sharply bounded sheet of rock. The margins of the dyke cut across the bands in the paler gneiss.

This tells us that the banding in the gneiss existed before the dyke was forced into it — in other words, the gneiss had been metamorphosed before the intrusion of the dyke.

From here, follow the track for about 200 metres and then turn left to follow the footpath signposted to Alltanabradhan. This path climbs steadily up through rocky outcrops. When you reach the highest point of the path, it is worthwhile diverting briefly to scramble up a knoll on the right hand side of the path, reaching a small cairn on the summit [2] [NC 06130 25497].

On a clear day, there is a panoramic view of the mountains of Assynt and Inverpolly — Canisp, Suilven, Cùl Mòr, Cùl Beag, and Stac Pollaidh. These mountains are composed of layers of red Torridonian Sandstone, standing proud above the Lewisian Gneiss. At one time, the Lewisian Gneiss would have been entirely covered by a blanket of Torridonian Sandstone, several kilometres thick, but now most of it has been eroded, leaving only these ‘inselbergs’ — island mountains.

The vegetation that covers the landscape today has appeared only since the last glaciers retreated around 10 000 years ago. This knoll is a good spot to look at lichen, some of the first vegetation that would have appeared. The three different groups of lichen, crustose (growing as a crust), foliose (leafy lichen) and fruticose (branched lichen), all grow close together here.

Continue along the winding path to a gate in a small valley. The path climbs from the gate and carries on over a small plateau, with boggy areas dotted with grasses and wild flowers including bog cotton, bog asphodel, lousewort and milkwort. Where you join a wider track, turn left and continue following the signs for Alltanabradhan, past rocky crags down to a small stream and the ruined Alltanabradhan meal mill [3] [NC 05389 26197].

You can still see the millrace flowing under the building, and the large flat millstones scattered around. Some of the millstones are made of red, pebbly Torridonian Sandstone that is clearly not local. The story goes that 130 years ago the miller, John MacLeod, travelled to Suilven to cut and dress his millstones. He then rolled and dragged them down the Kirkaig valley to Inverkirkaig, where they were loaded onto a boat and brought here.

From the mill, walk down the path to Port Alltan na Bradhan, where a beautiful beach is exposed at low tide [4] [NC 05099 26211]. The bay is ringed by low cliffs, speckled with thrift, sea campion, roseroot and sea ivory. If you wander across the rocky platforms and boulders around the beach, you can see that they are made of Lewisian Gneiss that appears more thinly banded than the gneiss at Achmelvich.

From here, the easiest way back is the outward route. However, there is a more adventurous route, only for those with sturdy footwear and during dry weather. Climb up on the south side of Alltanabradhan beach to reach a wide peninsula. Take care moving around in this area, especially if the rock is slippery. High above the sea on the far side of this peninsula, rock platforms and cliffs display fantastic folds in the gneiss. At high tide, listen and watch out for jets of water emerging from a blowhole low down in the cliff. From here, a faint path can be followed back along the cliffs — at several points it is possible to detour inland to meet the main path and return to the car park.

At low tide and in good weather it is well worth visiting the beach immediately north of Achmelvich [5] [NC 05851 25220]. This sandy cove is splendid in itself, but also contains some of the best exposures of Lewisian Gneiss — the closest thing to geological works of art!

Figures

(Figure 42) Achmelvich to Alltanabradhan Mill. Painting of walk by Elizabeth Pickett.

(Figure 43) Contorted banding in Lewisian Gneiss at Achmelvich.

(Figure 44) Scourie Dyke cutting gneiss by the track at Achmelvich.

(Figure 45) View of Canisp, Suilven and Cùl Mòr.

(Figure 46) Alltanabradhan Mill.

(Figure 47) Port Alltan na Bradhan.

(Figure 48) Lewisian Gneiss on the beach north of Achmelvich.