Drystane Dykes

One of the great aspects of the landscape of the British Isles are the field boundaries. They are a primary force in shaping what we think of as our countryside and they encapsulate both beauty and history whilst having arisen from practical necessity. Hedges and dykes make our fields more appealing to the eye, giving patterns to the strange shapes of historical land division. Hedges tend to inhabit the softer, cosier parts of these islands, whilst dyking complements a wilder landscape with its rough edges. For the most part, dykes are just  element in the scene, but in places like the Aran Islands and the Yorkshire Dales, the walls become the landscape and simply knock you out with the sheer effort required to build them. Not only is it the sheer effort in building them, but also the labour required to collect the stone in the first place.

Although dykes have character on a large scale, closer inspection shows a whole range of building materials and styles. To the geologist they are the vertical expression of a horizontal bedrock and an easy way to look at the rocks of an area. On Arran you can see this as you drive around, with the Sandstone dykes of the east and south and the Granite walls of the North and centre giving way to those of Schist in the Northwest. Each stone works in a different way and gives rise to its own style. Sandstone walls are neat and regular, with stones generally being laid down in courses and with neat coping (top) stones and hence this rock is one of the most popular to dyke with, especially in Scotland. Granite boulders are pretty hard to break up, so we get the amazing balancing dykes that you can see around Machrie and are single thicknesses of stone, rather than the usual double-skin approach. Known generally as Galloway dykes, because of the great numbers in that area, it is always said sheep see the holes and are afraid to try and jump the dyke because they look like they will topple over. The Schists are a kind of inbetween building material and you will see horizontal courses topped with courses balanced at angles, which make very appealing walls.

The Devonian and Cornish “hedges” are built often in a rubble type array, but the classic is the herringbone slate wall. The classic Devon hedges are hedgerow trees planted on top of a drystone wall. One of the most peculiar types of dyke are the stone fences of Caithness and Orkney, where the easily split Sandstone is laid like gravestones around the fields. In terms of wildlife all these old walls provide wonderful nesting habitats for birds, and a superb substrate for lichens and mosses, with rocks like schist providing more nutrients than the acid rocks like granite.

Whilst the UK may have its fair share of dry stone walls, it is not a uniquely British trait, although they may more often be seen in the form of terracing in other countries. Dyking was also exported to the colonies, and there are remnants in the East of Canada and USA, though the abundance of timber in the wooded areas of the States meant that a lot of fencing was constructed from poles rather than stone.

There are some curious dykes to be seen around Scotland. Many date from the time of the clearances when people were employed to build boundary walls between estates. There is a phenomenal one on Beinn Dearg near Ullapool, which extends up to around 3000ft in altitude. On Fetlar, in Shetland there is a Bronze age dyke that stretches across the island as well as the clearance dyke. One interested use of dry stone was to construct a lobster trap across a river on Great Bernera, outer hebrides.It was built in the 1860s and is still there, showing the strength of dry stone

To see a phot of the Great Bernera dyke and some other interesting dykes go to http://halfpie.net/article/150/