2016:639 - FORT MITCHELL, Spike Island, Cork

Monitoring of ground works was undertaken at various locations both in and around Fort Mitchell during a Cork County Council landscaping and service upgrade project on Spike Island. Permission to use of a metal detector to assist in artefact retrieval was granted under the Ministerial Consent. The majority of the landscaping works within the fort were limited to the removal of sod layers within disturbed areas and, where feasible, upgraded services were inserted into existing pipe trenches.

Construction of the existing fort commenced in 1804 on the site of an 18th-century fortification. The existing level ground within the fort was created by extensive 19th-century quarrying while the sloping ground outside the walls comprises a glacis constructed with the quarried stone. By 1822 the fort was still incomplete but a renewed building phase was instigated after the island was converted into a convict depot in 1847 and modifications continued to be made to the fort into the 20th century. It was handed over to the Irish Government in 1938 and remained as a military/naval base until the 1980s when it was granted to the Irish Prison Service. Substantial damage to areas of the fort subsequently occurred during the creation of prisoner control measures. This included the demolition of various structures as well as the removal of access to the bastions by a combination of new concrete walls and infilling access routes with soil and rubble.

The project entailed supervising the removal of modern infill material introduced by the Prison Service and landscaping was undertaken in areas formerly occupied by demolished 19th- and 20th-century structures. All exposed sub-surface remains of structural remains were recorded and left to remain securely in situ.

Bastion 3 (south end of fort)
Landscaping works on Bastion 3 involved the removal of a thin sod layer that had developed on top of a soil cover introduced following Prison Service demolition works. Occasional inclusions were noted under the sod layer and included plastic bags, bottles, tobacco pipe stems, three 20th-century Irish Army steel mugs and various 19th-20th-century pottery sherds. Monitoring of the construction of two access steps to the top of the bastion revealed 20th-century inclusions within the underlying soil cover. The upper section of a buried 1.5m wide concrete alcove feature was identified under the sod layer on the west side of the bastion (at ITM 580407, 564535). This may have been associated with a nearby gun emplacement visible on a 1963 aerial photograph. The exposed section of the alcove was recorded and it was then resealed. There were no traces of the demolished gun emplacement exposed under the sod layer but the presence of the alcove demonstrates the potential survival of other buried features in this area.

The removal of concrete rubble blocking the steps leading down to the conjoined Underground Shelter and Battery Observation Post under the centre of the bastion exposed the intact concrete steps. The interior of the concrete shelter and two passages leading to the observation post on the seaward side were also intact but contained no surviving internal fixtures or artefacts.

The concrete observation post on the seaward side comprised a curved space partially divided by a central north-south concrete wall. The roof was 2.18m above floor level and the overall internal area measured 6.04m (east-west) by 3.04m. The narrow observation slot on the seaward (south) wall had been sealed with concrete blockwork which was removed under supervision. The central dividing wall contained a mounted timber tidal gauge and painted datum information for various harbour landmarks. These features were recorded and will remain in situ. The interior of the observation post was found to have been cleared of material apart from a badly corroded metal stove, fuses and truncated cables. Cork County Council have arranged for the appropriate secure onsite storage of this material.

Walkway between Bastions 3 and 4
The removal of a deep infill of soil introduced by the Prison Service to block the former access route between Bastions 3 and 4 was monitored. This exposed the surviving basal courses of two 19th-century structures set into the earthen bank along the north side of the walkway. These comprise the remains of the cut limestone walls of a Small Arms Store and Forge Store shown on an 1894 survey of the fort. They are also visible in 1980’s aerial photographs taken prior to the Prison Service interventions. The exposed front facades of both buildings had been removed down to window sill level and loose limestone blocks were encountered within the soil infill adjacent to both structures. Cork Council arranged for the secure storage of these onsite. While not exposed, the roofs of both buildings under the bank appeared to have been removed and their interiors were completely infilled with rubble. The remains of both structures were recorded and their surviving facades remain in situ as visible features along the walkway.

Bastion 4 (south-east corner of fort)
The removal of the modern infill blocking the former access route on the inner (west) side of the bastion exposed the concrete roof of the underground bastion passage which had formed the surface of the access route. The removal of the infill in the north end of the bastion exposed a 1.8m wide, unroofed, sunken passage, with concrete side walls and a floor located 2m below adjacent ground surface. The passage is shown on the 1894 survey which labels three recesses revealed along the east wall as shell recesses and these will be left exposed as part of the reinstated walkway. The sunken passage initially extended 7.2m northwards and then turned to the north-west for 10.05m where it terminated at the entrance to the infilled stairwell leading down into the underground bastion structure. The removal of the concrete rubble which had completely sealed the concrete steps was carried out manually. A portion of the rubble appeared to have been created by the demolition of the concrete roof over the top of the stairwell entrance but the amount present indicated that some of the rubble was sourced from elsewhere, perhaps from demolished structures on top of the bastion. The removal of the rubble from the stairwell entrance also exposed the concrete steps leading down to an intact northern side gallery, the interior of which contained no surface artefacts or fixtures.

Bastion 6 (north end of fort)
The removal of the sod layer along a new footpath on top of Bastion 6 revealed an underlying spread of soil with modern surface inclusions. No surface traces of the gun emplacement shown in the centre of the bastion on the 1894 survey were revealed. A buried concrete feature was partially exposed under a spread of loose concrete rubble at the former location of 20th-century gun emplacement visible at the west side of the bastion on a 1963 aerial photograph. The rubble infill on the line of the footpath was manually removed and this partially exposed the buried remains of the concrete emplacement which comprised a surface platform with a central, sunken circular area. This feature was recorded and then resealed with soil.

The removal of the sod layer at the top of the two access ramps extending up to the bastion also exposed two munitions shafts extending down to the underlying magazine structure and these were retained in situ.

A small rectangular concrete surface (1.2m x 1.8m) was exposed under the sod near the centre of the bastion and its location corresponds to an artillery recess structure shown on the 1894 drawings. This feature was also recorded, resealed and remains in situ.

Parade Ground
The existing lawns, tarmac-covered roads and yards were created by the Prison Service in the 1980s and this included the removal of the existing yard surface and the introduction of topsoil sourced from the outside of the fort. Landscaping works in the northern end involved the removal of the thin sod layer in previously disturbed ground surrounding the extant Shell Store building adjacent to Bastion 6. A number of 19th-century buildings in this area were demolished by the Prison Service in the 1980s which are clearly shown on various historic maps that label their original uses. The fragmentary remains of a number of demolished structures were exposed beneath the sod and included the foundations of the Shell Store blast wall as well as remnant traces of the floors of an office building and various stores. All exposed sub-surface features were fully recorded, resealed and remain in situ.

Works in the north-east corner of the parade ground entailed the creation of a new exhibition structure within a modern prison yard enclosed by tall concrete walls. The removal of the tarmac yard surface revealed the random rubble foundations of two demolished walls and traces of a small concrete floor surface. These correspond to boundary walls and a shed structure shown on historic mapping and were recorded, re-sealed and remain in situ under the exhibition structure.

Ground works associated with upgrading of an early 20th-century canteen building, formerly used as a gym and a military drill shed, within the north-east corner of the parade ground were also monitored. Cartographic sources indicate that this area was undeveloped during the 19th century and monitoring of the removal of topsoil material introduced around the building in the 1980s did not reveal anything of archaeological significance.

The majority of the new services within the parade ground were inserted into existing pipe trenches and the only new section comprised a trench extending along the tarmac road on the north side. The modern road surface overlay a make-up layer composed of re-deposited subsoil and quarried bedrock fragments. This layer measured up to 0.8m above intact bedrock while it was absent in areas where the uneven bedrock surface extended close to road surface level. A number of modern services trenches were exposed and no traces of structural remains were encountered. There were very few inclusions within the make-up layer and these comprised brick fragments, chinaware sherds and modern objects.

It was deemed unsafe to excavate the section of the service trench exiting the fort through the confined northern gate passage so it was instead carried by 0.2m diameter bore inserted through the bedrock under the Casemate building adjacent to the west side of the gateway.

Fort Entrance Area and Glacis
The excavation of the service pipe trench continued in the area where the bore exited under the Casemate building as it emerged into an infilled rectangular walled moat centred on the fort gateway. This feature had been backfilled in recent decades with soil that contained frequent modern inclusions. The buried limestone block wall on the outer (north) side of the gate moat was encountered at a distance of 6.6m from the Casemate wall. It measured 0.95m wide at top and had widened to 1.9m at the base of the service trench where a 0.2m wide bore was inserted. The gate moat trench was backfilled with the excavated soil following the installation of the pipe. The area between the gate moat and the outer fort wall was infilled with a homogenous layer of quarried bedrock fragments, with occasional brick inclusions, that directly overlay natural bedrock. This material was similar in composition to the glacis fill encountered outside the fort and appears to form a continuation of this feature across the dry moat area. The quarried stone infill in this area gradually increased in depth from 2m at north to 4m at the outer wall of the fort. The quarried stone extended to the wall which may have been constructed on the underlying bedrock and the basal courses then sealed by the deposition of the quarried stones.

The pipe trench then extended down the north side of the external glacis towards a water treatment area in a low-lying field to the north-west. The glacis material was formed by a loose deposit of quarried bedrock fragments with localised lenses of re-deposited subsoils. The majority of the glacis was sterile although it contained occasional inclusions of 19th-century pottery, tobacco pipe stems and a localised dump of broken bricks. The service trench on the upper section of the glacis was excavated to 4m below modern ground level in order to tie in with the fall of the pipe as it exited the fort. The underlying bedrock was encountered in localised areas but for the most part the substantial deposit of quarried stone in this area was still present at the trench base. The depth of both the trench and the glacis material became progressively shallower as works extended downslope and the glacis material gradually tapered to 0.2m deep at its outer edge. The excavated stone from the trench was backfilled following the installation of the pipe.

Nothing of archaeological significance was noted during topsoil stripping at the water treatment area in the field adjacent to the base of the glacis.

Other Works
Monitoring of ground works undertaken for the installation of a shallow service trench along the northern coast road and the construction of a seating area on the modern surface of the landing pier did not reveal anything of archaeological significance.