2013:025 - Boom Hall, Ballnashallog, Derry

The 18th-century house known as Boom Hall, Co. Derry, stands within the townland of Ballynashallog, near the north-western bank of the River Foyle. The house takes its name from its close proximity to the boom constructed across the Foyle in 1689 by the Jacobite army during the second siege of Derry. The former park demesne associated with Boom Hall consists of an area of ground bordered to the north-west by the Culmore Road and to the southeast by the River Foyle. Most of this land is relatively flat, only sloping gently towards the Foyle, however, a strip of land about 35m wide and located immediately adjacent to the water’s edge forms a much steeper bank. In March 2013 an evaluative excavation was carried out in this steeper area in order to assess the suitability of the environs of Boom Hall as a site for a community-based archaeological project. The excavation was undertaken on behalf of the Northern Ireland Environment Agency.
The most archaeologically interesting phase of activity within the Boom Hall landscape is the military activity associated with the two 17th-century sieges of Derry. Unfortunately, no significant remains of this military landscape are readily identifiable on the ground, probably as a result of landscaping associated with the 18th-century park. Cartographic evidence suggests that within the immediate vicinity of Boom Hall the military features include Charles Fort, built by Royalist forces in 1649 during the first siege of Derry and reoccupied during the second siege of 1688-89 by Jacobite forces intent on maintaining a blockade of the city. In order to prevent ships delivering supplies to the city, the Jacobite army built a boom across the Foyle. The boom’s western end was located somewhere within the north-eastern part of what would subsequently become the Boom Hall demesne. In addition to the reoccupied Charles Fort, the western end of the boom was also protected by the creation of a bastion (sometimes known as the New Fort) and several adjacent entrenchments. These military features are best represented in a siege map entitled ‘A New Map Of The City of Londonderry with its Confines; As it was besieged by the Irish Army in the year 1689. Exactly Survey’d by Capt. Francis Nevill’ which dates to c. 1694 (Black 1990, 89-90, no. 82; Ferguson 2005, 24, no. 67).
Further insight into the arrangement of the Jacobite siege works associated with the western end of the boom, and independent confirmation of the accuracy of Nevill’s map, is provided by an account of the French engineer, Mons. Pointis, who was responsible for its construction. Writing on 14 June 1689 from ‘The Camp before Londonderry’, Pointis reported that ‘the banks of the river being raised with a very steep slope I have had entrenchments dug in the form of an amphitheatre one above the other where our troops which will be stationed there in such numbers as are needed will be safe even from artillery, not only because of the parapet but from the depth in the earth’ (trans. J. Wallis; quoted in Milligan 1946, 16-17). Pointis’ description of ‘entrenchments dug in the form of an amphitheatre one above the other’ located on the ‘very steep slope’ of the river bank is consistent with the depiction upon Nevill’s map of the series of three entrenchments aligned north-east/south-west in parallel with the Foyle and located between, on one side an L-shaped entrenchment and stream crossed by a bridge, and on the other side by a bastion built on the water’s edge. The description supplied by Pointis that the entrenchments were ‘dug’ and that the soldiers using them would be safe because of their ‘depth in the earth’ suggests that an archaeological trace of the entrenchments as a series of negative features should survive, even if the banks associated with the siege works were slighted following the lifting of the blockade and any surviving topographic expression of the features was compromised as a result of 18th-century landscaping.
The apparent position of the ‘amphitheatre’ of entrenchments can be identified in the modern landscape with a reasonable degree of confidence, if not absolute certainty. There is only one significant stream located on the western bank of the river between Madam’s Bank and Brook Hall - it discharges into the Foyle at Irish Grid Reference C45261980 and is represented on Nevill’s map as being crossed by a bridge close to the Foyle’s edge. This bridge was presumably built by the Jacobite army in order to facilitate movement between their headquarters at Brook Hall and Charles Fort. The footings and part of the span of a bridge still survive towards the mouth of the stream (Irish Grid Reference C45241978). Although it is possible that this bridge was newly built in the 18th century as part of a partially surviving, tree-lined drive that formed part of a circuit around the park at Boom Hall, it is just as likely that the surviving remains are those of the bridge depicted on Nevill’s map as being located immediately adjacent to the western end of the boom (and which was subsequently incorporated into the 18th-century drive). If this is the case then the ‘amphitheatre’ of entrenchments must have been located immediately to the north of the stream upon the steep slope of the bank running down to the Foyle. It is within this area (centred upon Irish Grid Reference C45251980), now overgrown and planted with mature trees and therefore not suitable for geophysical survey, that it was decided to excavate two trenches in order to attempt to verify the position of the ‘entrenchments’ and assess their archaeological potential.
Trench One was aligned roughly north-west/south-east, with the south-eastern end of the trench being located immediately adjacent to the demesne wall bordering the River Foyle. The trench was 10.6m long and 0.8m wide. Underlying the topsoil at the south-eastern end of the trench was a thin deposit of sandy loam, which in turn sealed an apparent hill wash deposit that extended throughout the trench. The apparent hill wash contained numerous fragments of coal and some blackware pottery suggesting that it had accumulated at some point during the 18th to early 20th century, possibly during a period when the field above the trench was being cultivated. Excavation of the hill wash revealed that, in the north-western half of the trench, it directly overlay the surface of the bedrock, whilst in the central part of the trench it overlay a layer of sandy clay loam that contained occasional brick fragments, and 18th-century pottery and bottle glass. How this latter deposit came to be formed is uncertain, however, it may represent another deposit of hill wash. Towards the base of the sandy clay loam an undeformed lead, or lead alloy, musket ball and a gun flint were recovered. These finds are interpreted as relating to the 17th-century military activity in the area. For most of its extent this possible hill wash directly overlay the surface of the bedrock, however, its south-eastern edge overlay a thin natural subsoil of compacted gritty clay. At the south-eastern end of the trench the natural subsoil had been cut by a steep edge that also passed through the bedrock for an excavated depth of 0.76m. This steep edge is interpreted as a rock-cut feature. Although only exposed in a 0.8m wide trench, this steeply cut edge was observably aligned on a near east-west orientation. Only the northern half of this cutting was exposed in the last 0.6m of Trench One. It was filled with a thick deposit of yellowish gravelly sand that contained at least one concentration of shell and which probably represents the deliberate deposition of material derived from the nearby shoreline. Although mostly sterile, this gravelly sand contained a fragment of possible roof slate and a sherd of blackware pottery. It overlay a dark brown silty clay that probably represented an in situ soil horizon and which contained a large sherd of Buckley blackware dating to the 18th or 19th century. It is uncertain what this artificial edge represents. Although it may have been part of one of the Jacobite entrenchments, its apparent east-west alignment is not consistent with the north-east/south-west alignment of the entrenchments represented upon Nevill’s siege map. A more likely explanation is that it represents a low-cliff edge, initially created as a result of natural erosion associated with either the adjacent stream or the River Foyle and then quarried to provide stone for the adjacent demesne wall. The hole created by this quarrying was left open enabling an 18th- or 19th-century soil to develop, before it was deliberately backfilled with material derived from the adjacent shoreline.
Trench Two was aligned roughly north-west/south-east with the north-western end of the trench being located immediately adjacent to a modern field boundary just below the cusp of the steep slope down towards the Foyle. The trench was 0.8m wide, 15m long and was positioned upslope and to the west of Trench One in an area where the ground surface of the natural slope was uneven suggesting the former presence of earthworks. Underlying the topsoil was a gravelly clay deposit that was interpreted as representing a natural subsoil that had been disturbed by root action and animal burrowing. Excavation of a small sondage into this deposit revealed that it only had a maximum depth of 0.06m before it became a ‘clean’ natural bright-orange sandy clay subsoil. At the north-western end of the trench, the removal of the topsoil revealed evidence of two cultivation furrows, approximately 0.25m wide and aligned approximately north-west/south-east. The position of these features, which were not excavated, lay just beyond the outer edge of a positive lynchet that had formed across the line of the modern field boundary. The gravelly clay deposit of disturbed natural subsoil extended throughout Trench Two except for a complex negative feature which excavation demonstrated was a tree throw that had been filled with a complex succession of hill wash and silt layers, some of which had supported the growth of vegetation and consequently had a dark, almost peaty, organic character. Undoubtedly, the uneven character of the overlying ground surface, which had suggested the sighting of Trench Two’s position, was a direct result of the tree throw.
The results of the excavation were disappointing in so much that no unequivocal evidence for the Jacobite entrenchments represented on Nevill’s siege map was uncovered. On reflection, it may be that the trenches were located too close to the stream identified as that being crossed by the bridge in Nevill’s map. That said, the recovery of lead, or lead alloy, shot and a gun flint from Trench One strongly suggests that the trenches were located close to the sought-for area of 17th-century military activity. In addition, it is also possible, but not probable, that the rock-cut edge identified towards the south-eastern end of Trench One represents the back edge of one of the Jacobite entrenchments. Further excavation will be required to interpret this feature with absolute certainty.
References
Black, E. (ed.) 1990 Kings in Conflict. Ireland in the 1690s. The Ulster Museum, Belfast.
Ferguson, W.S. 2005 Maps & Views of Derry 1600-1914, a Catalogue. Royal Irish Academy, Dublin.
Milligan, C.D. 1946 The Relief of Derry. Browning and the Boom. Its Making and Its Breaking. Londonderry Sentinel, Londonderry.
Philip Macdonald, Centre for Archaeological Fieldwork, School of Geography, Archaeology and Palaeoecology, Queen’s University, Belfast, BT7 1NN.

Centre for Archaeological Fieldwork, School of Geography, Archaeology and Palaeoecology, Queen’s University, Belfast, BT7 1NN