HS2 Phase 1 - Central Section, Archaeological Works, M25 Access Slip Roads (1C17MSRTT) Trial Trench Report

Trial Trench The test pit and trial trench evaluation was undertaken on land located either side of the M25, to the east of Chalfont St. Peter, to assess the archaeological potential of the Site to contain artefacts, deposits or features of archaeological significance, particularly those of huntergatherer, Late Glacial or Mesolithic activity, for which the Colne Valley is nationally renowned. The Site comprised three land parcels (Fields 1 - 3) measuring c. 5.1ha to the west of the M25 (Field 1) and 9.7ha to the east (Fields 2, 3). The land is required for the construction of access slip-roads and 'bell-mouths' which will allow access to the Chiltern Tunnel South Portal main construction compound and construction site located to the south. The Site is located in the vicinity of cropmark evidence for ditches and pits relating to prehistoric and/or Romano - British activity and the route of a possible Roman road and lies within the wider archaeological landscape of the Colne Valley. As such it has potential for the survival of archaeological remains of Mesolithic to Roman date. In addition to trial trenching, three test pits within the footprints of the evaluation trenches were sample dry-sieved, to the full depth of the ploughsoil, for retrieval of artefacts and identification of finds scatters, particularly lithics. A moderate assemblage (943 pieces) of worked flint was recorded of which the majority comprised debitage of Neolithic/Bronze Age date with a minor component of blade/bladelet technology usually indicative of a Mesolithic/Early Neolithic date. Only four 'truncations', a diagnostic Mesolithic artefact type, were recorded from Fields 1 and 2. A bladelet core was also recorded from Field 1. Most of the 18 cores and 10 scrapers recovered from the evaluation were of diagnostically Neolithic and Bronze Age date. Relative concentrations of lithic artefacts were recorded on the margins, or within the dry valleys crossing all three fields. The lithic assemblage and its spatial distribution would indicate episodic and ephemeral Mesolithic and Neolithic/Bronze Age activity on site, associated with the use of the dry valleys as corridors of movement between the River Colne floodplain and the hinterlands beyond. Only a small number of pits and ditches were recorded from the evaluation, which mostly comprised post-medieval and modern quarry pits. The quarry pitting was for the extraction of the prevailing natural gravel geology over most of the higher ground of the site, which is known from the historical mapping of the area, as well as from a geophysical survey to the immediate south of Chalfont Lane, to be quite extensive 19th - early 20th century extraction. Other features included a small Neolithic/Bronze Age pit from the north of Field 1, two small prehistoric pits in the south of Fields 1 and 3, a small Early Iron Age pit in Field 3, and a possible rectilinear array of Late Iron Age/Early Roman ditches in the south of Field 1, which probably represent part of a field system.