SDO9597 - St John Ambulance Hall, North Square, Dorchester, Dorset: Archaeological Observations of Structural Engineer’s Test Pits

Following the archaeological evaluation of the St John Ambulance Hall site in February 2000, an arrangement was reached with the structural Engineer that the Engineer's test pits would re-use the archaeological evaluation trenches.Two of the testpits excavated during the archaeological evaluation had not been bottomed and so were further excavated as structural engineering test pits under archaeological supervision. The watching brief was conducted by Terrain Archaeology for Signpost Housing Association in March 2000. No new archaeological deposits were observed in Trench 2. In Trench 4 no deposits earlier than the 19th century were exposed. Probing the base of the testpit indicated that the top of the natural chalk was about 3.4 m below the surface. The observations have revealed the existence of in situ archaeological deposits below 1.6m of 19 and 20 century soils on the eastern part of the site. Unfortunately the nature of the investigations means that it is almost impossible to interpret these deposits on present evidence. The great depth at which the chalk bedrock was encountered in Trench 4 suggests that the trench might have been located above a feature, perhaps a pit or ditch, cut into the chalk. The fact that the natural chalk was encountered at a height about 1.3m above this level, further down slope in the rear of St John House lends credence to this hypothesis.