Natural History of an Excavation
Layered sand with fault.
Steele, in his 1836 book "Beauties of Gilsland" wrote:
“The road leading from Gilsland to Glenwhelt . . passes between two conical-shaped hills apparently formed by art . . These eminences are supposed by antiquaries to be Danish, but history and tradition are alike silent respecting them.”
I should think they are. The surrounding area is festooned with conical mounds, and more evidence than their mere existence is required to invest them with historical significance. Even though the mound in question, at the entrance to Irthing Park, could look slightly conical from certain angles, it is in fact an elongated ridge with a slightly higher section (now removed) at one end. (In much the same way, the Moat at Brampton looks like a conical hill from the south, but is the end of a long ridge – which is itself an esker, a special type of glacial deposit – but that’s another story.)
In October 2005, the conical west end of the ridge running along behind the houses of Rose Hill (road) was excavated to provide space for a building development. About 8000 tonnes of material were removed, much of which was processed by Thompson’s of Prudhoe for sand and gravel. Such deposits are the norm in this area, but as the exposed faces of the excavation have weathered, unusually clear details of the layering within the mound have become increasingly visible, especially in the north and east faces. The south-east part seems to be much more amorphous and sandy.
The north face shows interleaved layers of sand and gravel, becoming sandier towards the east. The gravel is poorly sorted. The pebbles within it are rounded and of many different types of rock. All the visible strata are steeply sloping. Sixteen very large boulders (100-150 cm) uncovered during the excavation are now in the village playground, helping to stabilise a steep slope of similar material on the side of the original Rose (or “Raise”) Hill, where the station now stands. Looking more closely at the exposed north & east edges of the excavation, the thick deposits of pure sand can be seen to be finely layered, with miniature faults cutting the layers. These layers look to me like the formations seen within sand-dunes, suggesting that this material was deposited by the wind. All of this evidence is strongly suggestive of deposits laid down either by melting glaciers or in a periglacial (close to an ice-cap) environment:
- Poorly sorted mixtures of rounded but different-sized rocks are indicative of chaotic, fast-flowing rivers carrying a heavy load of aggregates;
- The mixture of different rock types is characteristic of glacial till;
- It is difficult to think of a mechanism by which enormous boulders could become mixed in with deep deposits of sand and gravel, except by being dropped by melting ice;
- Dry, unvegetated desert-like areas with wind-blown sand are typical of polar regions close to ice-caps.
Whatever the precise process that gave rise to the formations seen within the mound, it is pretty certain that it was some kind of natural deposition. If the hill had been “formed by art” the contents would be unlikely to show the fine bedding seen in the sand and the rest of the deposit would be more evenly mixed if people had laboriously accumulated barrow loads or baskets of soil from elsewhere. Big burial mounds are not typical of this area and whereas hills were sometimes created or enlarged as a foundation for small defensive structures, there are so many natural mounds hereabouts that further evidence is required to single one out as man-made. This particular one was probably selected because remains of a fort and a Roman carving were found on the nearby summit of Rose Hill when the railway station was built there. The odd shape of this and other hills within the village are probably due to the dissection of larger, more smoothly rounded hills by flowing water, either the Irthing or Poltross running at higher levels in the distant past, or short-lived meltwater streams from receding glaciers.
At the end of April 2006, the upper, sandy stratum of the north face was colonised by numerous sand martins (Riparia riparia), the number of burrows rapidly increasing to over 100. This was of great interest for a variety of reasons, as these birds, while not rare, are specialists and are usually only found nesting in their preferred habitat of river banks or similar sandy banks close to water. The Irthing Park site is also subject to disturbance, with cars, people and occasionally diggers in close proximity, but none of these seem to worry the birds at all. Apparently Sand Martins often nest in the walls of active gravel pits, and colonies are known to desert their nesting sites and move to fresh ones, a necessary adaptation to life in unstable sand walls.
They are migratory, spending the winter in the Sahel region of Africa, where droughts can result in sharp falls in numbers. In the summer they are found throughout Europe, with some particularly large colonies in the banks of the great rivers of Hungary which are sometimes destroyed by summer floods. Numbers of these birds are therefore likely to fluctuate from year to year, as the BTO website says:
“This species is notoriously difficult to monitor, because active and inactive nest holes are difficult to distinguish, and because whole colonies frequently shift to new locations as suitable sand cliffs are created and destroyed. Waterways Bird Survey nest counts suggest a stable or shallowly increasing population, with wide fluctuations, and a steep decrease in the last seven years. BBS counts of birds show steep declines in the UK and England since 1994. Winter rainfall in the species' trans-Saharan wintering grounds affect annual survival and thus abundance in the following breeding season”
As we have all seen, the changing climate has caused not only drought in the Sahel but changes in the behaviour of our rivers. Spates are becoming more dramatic, and a landslide somewhere along the Irthing may have dispossessed this colony. Whatever the causes of habitat creation or destruction, Gilsland is the richer both for an influx of such fascinating visitors, and for a peep into the processes which formed our unusual landscape.