The pattern of throughstones varies considerably between areas.
Projecting throughs
One of the more noticeable variations is whether or not the throughs project. In many areas throughs project from both sides of the wall from 1″ (25mm) up to 6″ (150mm).
Beyond tradition, there are various explanations for this practice. In the Derbyshire High Peak, and in the slate areas of Wales and the Isle of Man, throughs which project 6″ (150mm) or more are used to dissuade sheep from jumping. In sandstone areas, longer throughs may be used as they are, rather than trying to dress the ends and risk cracking them at inconvenient points.
Another possibility is that projecting throughs are used so that as the wall settles and widens, the throughs will still serve to bind the faces together.
Occasionally throughs project from one side of the wall only, being flush on the side adjoining tracks and paths. This may be to lessen the chance of them being knocked, or to discourage unwanted access and damage to the wall. On a slope, the projection is more likely to be on the downhill side. This may be because any settlement will be downslope, and thus the throughs will still bind the faces. Another reason is that if projections have to be made, putting them to the downhill side is less likely to give access to sheep than if they were put on the uphill side.
‘Single projection’ may also have been used to indicate ownership of a boundary wall, or for appearance on estate walls. Many walls around reservoirs in Northern England owe their distinctive appearance to projecting throughs and three-quarter throughs.
Absence of throughs
The use of throughstones in a wall is generally regarded as an essential part of their structure, but there are many long-standing walls which disprove this rule.
In the Craven district of Yorkshire throughstones are rare, but the blocky limestone binds firmly together without throughs, and settles into a more durable wall than many more regular types of stone. In Aberdeenshire throughs are normally absent, as stones of the available thickness which could span the wall would be too heavy to lift. Instead the size and weight of individual stones keeps the whole structure stable.
Similarly walls built of large bouldery stone rarely have a formalised pattern of throughs. Unlike walls built of smaller stone, which have two faces filled with hearting and joined by throughs, boulder walls have essentially two faces which join, with many boulders acting as three-quarter throughs.
Walls without throughs are often wider at the base and have a greater batter than would otherwise be the case. Whether this is a conscious design feature to aid stability, or has resulted from the need to fit very large stones in the base is a matter of conjecture.
Flush throughs
Just because a wall does not appear to have throughs does not mean they are not there. Throughs are often built flush to stop cattle rubbing on them and loosening the wall, and are thus difficult to recognise. When rebuilding, flush throughs should be replaced flush, although with repairing gaps, this may mean replacing them lower than they were originally. This is because the stones of derelict walls, and especially the hearting, tends to ‘disappear’ through being trampled in or broken, and unless more stone is brought in, the wall will need to be built narrower than it was previously. To span the wall, the flush through will thus need to be placed lower.
Escaping sheep tend to ‘run up’ the face of a wall at an angle, rather than face on, and projecting throughs can act like steps to make escape easier. This tends to refute the argument that a consistent pattern of well-projecting throughs acts as a deterrent. Projecting stones probably only act as a deterrent when they are used in the coverband, where they both look, and are, awkward to clamber over. Stockproofing depends on many factors, including the flatness of the face, the batter, the overall height of the wall, and most importantly, the nature of the sheep in question. The occasional projecting through will certainly aid a determined hill or mountain breed to scale a wall.
Flush throughs can follow any of the formal patterns outlined below, which require trimming individual throughs to fit. Trimming can be difficult with some types of stone, so formal patterns are more suited to slates, mudstones or thinner sandstones which are easier to trim.
Flush throughs can also be used without trimming, by fitting them at the appropriate height for individual lengths to span the wall exactly . This will not be as strong as fitting throughs at regular intervals along a course, but helps to strengthen the wall. Spread the throughs as evenly as possible along the length, staggered with height to fit. An even spread is important to ensure even settlement, as sections without throughs will settle differently from those with throughs, in extreme cases ‘peeling away’ and collapsing.
Patterns
For walls with throughs, one or two rows are normal, depending on the wall’s height. Around the Derbyshire High Peak, both limestone and gritstone walls have three rows of throughs, as have many walls in North Yorkshire and Cumbria. In the Northern Pennines, on the north side of the A66 in Stainmore Pass, a few very tall limestone walls contain four rows of throughs.
The pattern of throughstones in an area can be remarkably consistent, usually because the spacings have been specified by an Enclosure Award.
In some areas walls contain a complete layer or layers of throughs, with the throughs butted up against each other in the layer. This is particularly noticeable around Langwathby in the Eden Valley, where large flat sandstone throughs bind two skins of small rounded stone. The efficacy of complete layers is open to question, as discussed below.
Complete layers may work better than spaced throughs as both sides are tied for their entire length. Also, the stonework above is less likely to settle unevenly, as it is built on a level bed of stone. However, some wallers maintain that the butted throughs effectively divide the wall into two or more independent layers of stonework, and if the wall settles unevenly across its width the throughs will tilt and shed the stonework above them.
There is also some evidence that the stones below a complete layer of throughs tend to work loose. This is because small stones get used for levelling up the stonework to make a base for the throughs to sit firmly, and these stones may settle unevenly. Where throughs are spaced, the wall becomes an integral structure for its entire height.
In many areas, particularly the sandstone areas of Northern England, many walls have complete rows of throughs below the coping, which are known as covers or coverband.
The availability and nearness of suitable stone is always a factor in the pattern of throughs. The walls immediately around Middletongue Quarry, a disused sandstone quarry near Greenhow Hill, North Yorkshire, have two rows of projecting throughs and a large projecting coverband. As distance from the quarry increases, the frequency of throughs decreases, until only a mile from the quarry, there are few visible.
Other points
Throughs of different stone
In some areas, throughs of a different stone type are imported. This is noticeable on the borders of limestone and sandstone areas, such as the edges of the Craven fault, where sandstone throughs are common in limestone walls. Here sandstone is also often a component in the wall heads. If you look closely at these walls, you can find runnels in the faces of some limestone beneath sandstone, where rainwater dripping off the more acidic sandstone dissolves the limestone. These runnels indicate that the wall is probably several centuries old, as the process is very slow.
Slate throughs are also sometimes used with other stones. In parts of Wharfedale and much of Ribblesdale (Raistrick, 1966), throughs were split from large glacial erratics of Silurian slate, as the predominant local stone is too rounded to use for throughs. A similar practice occurs in the Duddon Valley in the Lake District. However in areas where sandstone throughs are available, they tend to be used in preference to slate, which is more liable to fracture.
Great care needs to be taken when mixing flat throughs with rounded or irregular building stone, as it can be difficult to provide a firm, level bed for the throughs.
Mortar bands
In place of throughs, a layer of mortared stones is sometimes used, as in this example from Portesham, Dorset. Although this may seem a valid technique to use where throughs are not available, it’s likely to cause the same problems as a complete layer of throughs, and is not generally recommended. The stonework beneath the mortared layer may also settle, leaving a gap as with mortared copes. In this example a lime mortar has been used, which is more flexible than the normal cement mortar, and may be less likely to cause problems.
