12 June, 2015

A Tale of Two Troughs

Tim Coughlan discusses an Early Bronze Age burnt mound in Roscommon which displayed interesting evidence for phasing and woodworking.

Advance testing along the route of the N61 Ratallen Road Realignment Scheme in Co. Roscommon identified a burnt mound at Ratallen 1 (Licence Ref.: 12E264) which was subsequently excavated over the course of a sunny week in May 2013 (Licence Ref.: 13E0126).

The site was located at 110m OD to the immediate west of the existing N61. Approximately 14m to the south a small stream forms the boundary between Ratallen and Runnaboll townlands; in the parish of Kilcolagh. The stream is shown on the first edition six-inch Ordnance Survey map (1838) and the surrounding lands, including the site of Ratallen 1, are shown as marshy waterlogged terrain. A geophysical survey had been carried out in this area which failed to identify any anomalies of potential archaeological significance. The surrounding landscape is typified by small lakes and boggy marginal land and these settings often reveal temporary settlement activity; such as burnt mounds or fulachta fiadh.

The archaeological remains at Ratallen 1 comprised a truncated burnt mound positioned on undulating marginal terrain. The burnt spread measured c. 11.2m x 7m with a maximum depth of c. 0.47m and was visible as a low mound in the field prior to excavation. The site was associated with two phased, overlying wood-lined troughs.

The primary trough was located in a sub-rectangular cut which was cut through the natural peat layers and was oriented north–south. The base of the trough was lined with four timbers surrounded by a deposit of charcoal rich grey silt. These timbers contained mortices at both ends and wooden stakes had been driven through many of the holes to prevent lateral movement. The stakes may also have supported the walls of the trough although no wall remains or definitive indicators as to the nature and form of the walls was identified. Analysis of charcoal from the fill of the primary trough and of the timber remains was undertaken by the environmental specialist, Dr. Ellen O’Carroll. The results revealed that both alder and oak had been used as fuel for the fire and in the construction of the trough. Wooden stakes were identified as hazel, pomoideae and oak.

The secondary trough was located directly above the exisiting primary trough and was set in a sub-oval cut. The eight timbers were laid east–west, at right angles to the underlying trough timbers. There was no evidence that the timbers had been worked. A series of stakes were evident surrounding the base and it is felt that these may be related to a wicker lining/wall of the trough. Analysis of the charcoal remains revealed a dominance of alder, with hazel, ash, pomoideae and blackthorn in lesser quantities. Alder was also the dominant wood used in the construction of the trough lining while the stakes were largely hazel with some ash and pomoideae.

Wood samples from the primary and secondary trough returned two-sigma calibrated AMS dates of 2453–2143 BC and 2290–2041 BC, indicating the burnt mound was in use during the Early Bronze Age. These dates also suggest that there was a relatively short period of time between the individual phases of use at Ratallen.

O’Carroll identified evidence of woodworking from the primary trough including splitting, carving, through mortices and tool remains, such as one partial jam curve. The timbers lining the trough were irregularly and transversely split. All of the irregular splits were alder and ash, while the transverse split was oak. Wedge pointed ends were more common and metal axes with a slightly curved blade edge and blade width of 3.1cm in minimum size were used. No significant woodworking was evident on the upper timbers. The presence of through mortices on timbers from burnt mounds, such as those from the primary trough at Ratallen, are rare.

The analysis of the environmental wood, charcoal and peat samples confirmed the marginal nature of the surrounding landscape which consisted of a fen peat environment where reeds and alder trees would have grown. Alder favours wetter marginal conditions and the dominance of alder in the species used for fuel and construction of troughs indicates that it was readily available to the occupants of the site. It is likely that the alder and oak tree stumps identified to the north and south of the troughs could have been the source of some of the timber used on the site. Pollen evidence from a core analysed 20km north of Ratallen indicates a rise in alder pollen during the Early Bronze Age periods which compares well to the identifications at Ratallen.

While the identification of Bronze Age burnt mound activity at Ratallen 1 is not unexpected, when placed in context of the surrounding physical landscape, it is important locally as it represents the first documented evidence of prehistoric occupation in the immediate area.

Tim Coughlan, Senior Project Manager, tcoughlan@iac.ie