Dry stone walls reflect the bedrock or glacial drift material which lies beneath them. Originally built with what came to hand during field clearance, few field walls were important enough to warrant the transport of stones over any great distance. The Enclosure Era blurred the lines slightly, as for example on the borders of the Craven district of Yorkshire, where sandstone ‘throughs’ were sometimes transported several miles across country to use in the limestone walls. In the Cotswolds, much walling stone was produced as a by-product of building-stone quarries located some miles away. On the whole though, even during the most intensive period of new walling, most stone was quarried very close to the lines of the walls. Stones were carted, carried or sledged downslope to the work site, with small quarries being constantly opened and abandoned as the wall progressed.
With modern transport, some walls, particularly new or rebuilt roadside walls have lost their distinctive local identity as stone is transported over greater distances. In the Lake District, for example, there has been much rebuilding in cut slate supplied by a few big quarries. Although cheaper and quicker to build, these walls can look quite foreign to those of different types of stone or local slate. Generally though, the policy is to try and blend new work with old, so that the two can hardly be distinguished once the harsher angles and different colour of new stone have weathered and aged. There are often unavoidable differences with new stone, as modern quarries may have stone of a slightly different character from older quarries in similar stone.
Despite these qualifications, dry stone walls provide an excellent introduction to local geology. At the same time, geology reveals why the walls are there in the first place, and why they take on rather different forms in different areas. This connection between local geology and dry stone walling is developed in the following section.
The simplified geological column below helps put into perspective the approximate ages of the various types of walling stone mentioned in this handbook.
Virtually all stone used in this country for dry walling dates from the Jurassic Period or earlier, although Cretaceous materials such as flints are found in mortared walls in southern England, where more suitable stone is generally lacking. The most important types of stone for dry walling include Jurassic and Carboniferous limestones, Triassic, Permian, Carboniferous and Devonian sandstones, Silurian, Ordovician and Cambrian slates and shales, Precambrian metamorphic rocks, and volcanic and granitic and other intrusive rocks of various ages.
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