1997:162 - DUBLIN: Osmond House, Ship Street Little/Ship Street Great, Dublin

A preliminary appraisal was carried out to assess the impact of the substructure and associated works for two proposed small new wings forming an extension to the rear of the existing block at Osmond House, Ship Street, Dublin 2. Limited archaeological test-trenching was undertaken in each area but the scope of the investigation was constrained by the restricted height of the entrance access and the need to use a mini-excavator with a maximum reach of 1.8m.

At the south-west of the site, where the western wing is proposed, a steep, 4m-high bank of material exists on the site sloping towards its southern boundary. It was not possible to test-trench this bank as its slope was too extreme and the mini-digger could not manage the great depth of material it contains (much of its content may be loose rubble).

The site lies in an area of the highest archaeological sensitivity, adjacent to Dublin Castle and south of the city wall, city ditch and the original bed of the River Poddle. Immediately to the west, pre-development excavation in 1994 yielded evidence for a very deep accumulation of medieval deposits adjacent to the Poddle, which was diverted around 1174, based on Claire Walsh's results at Patrick Street. After that date a series of habitation levels with plank-built structures accumulated on the site until around the mid-13th century. Subsequently, the area appears to have seen several episodes of dumping and, where excavated, the dumped material is a very sterile, compact silty clay. It was supposed that the apparently rapid, final accumulation of material overlying the lower archaeologically rich sequence may have been derived from dredging operations. It is recorded that the Poddle and 'Pool' were prone to silting, giving rise to a possible need for dredging to ensure an adequate flow of water to the mill-races which it served (Linzi Simpson, pers. comm.). This also served the function of raising and filling an area, which is likely to have been very wet, adjacent to the Poddle bed. Tanning activities represented by wood-lined and barrel-lined pits in these uppermost fill deposits are thought to date from the 17th century.

The large site on which the church and graveyard of St Michael le Pole, excavated in 1981, is situated lies adjacent to the south. The church was located at the southern end of that site. Test-trenches closer to the site detailed in this report yielded evidence for late medieval deposits, but these were relatively shallow in the two areas tested, each of which lay more than 20m from this proposed development. There is a very marked difference in level between the sites, with a 4m drop onto the yard surface from the site boundary at its south-western side which is likely to reflect a significant underlying topographical change in level.

Two test-trenches were opened, one under each of the two proposed wings at the rear of the present building. Because of the need to use a mini-digger, the results of the test-trenching were not particularly informative, but coupled with information from the excavation conducted by Linzi Simpson on the adjacent site to the west, and the geotechnical site investigations report, an interpretation can be suggested and an impact assessment of the proposed structural design presented.

The quite low-grade archaeological clay soil exposed is very similar to that recorded on the adjacent site at the top of the archaeological profile within the excavated cutting (unpublished report by Linzi Simpson, 1994). In that location a deep accumulation of redeposited clay overlay a sequence of habitation features and deposits which built up over the dry bed of the diverted river.

Several elements of the proposed design gave rise to significant ground disturbance and alteration. In particular, preparation for the proposed retaining wall at the southern and south-western boundaries of the site necessitated significant excavation in an area which was not available for investigation for operational and access reasons.

Ground preparation and construction works for the foundations of the building were monitored by Edmond O'Donovan (see Excavation 1997, No. 163). No archaeological deposits of significance were breached, though the uppermost clay was exposed on a number of locations. Furthermore, the removal of the bank of material at the south-west of the site revealed no archaeological soils in situ.

Rath House, Ferndale Road, Rathmichael, Co. Dublin