The Shaugh Moor project is concerned with an area of moorland in south Dartmoor north-east and north respectively of the villages of Shaugh Prior and Wotter (fig. 1). The physical threat to the evidence for settlement and land-use caused by the operations of the China Clay industry involved the Central Excavation Unit of the Department of the Environment from 1976 in a programme of survey, excavation and environmental studies related to the settlements, land boundaries, burial mounds and ceremonial structures that are to be found on this piece of moorland. The background to the project and its preliminary research strategy have been outlined in Paper I (Wainwright et al. 1979) and this publication describes the investigation of a stone-walled enclosure surrounding houses and other structures that was totally excavated in 1977 and 1978. Subsequent papers will describe the related archaeological and scientific investigations into the past environment and land-use of this block of moorland and its adjacent region.

Isotope techniques have been applied to a study of groundwater movement in the Chalk of the London Basin. The 'age' of the water as determined by •4C measurements increases toward the central confined part of the basin where it exceeds 25,000 years and therefore originated during the Pleistocene. The age distribution supports previous interpretations of the permeability pattern, partly based on hydrochemistry. Measurements of tritium and the Stable isotope ratios of carbon, oxygen, and deuterium were also made. The •aC?2C ratio varied from -13%o at outcrop to values less negative than .-19oo in the central part of the basin, which is approaching the value of +2.35%o for the aquifer matrix. The •80 and deuterium ratios indicate that the Pleistocene waters were recharged at a mean air temperature less than 1 øC cooler than that of present day recharge, probably because recharge in the Pleistocene was limited to summer periods because of frozen ground in the winter. INTRODUCTION The London Basin is a synclinal structure in Cretaceous and Eocene strata in southeast England (Figure 1). The principal geological formations and their general thicknesses are [Water R'esources Board, 1972]' for the Eocene, London clay, 60-160 m, and Lower London Tertiaries, 12-40 m; and for the Cretaceøus, Chalk, 180-250 m, Upper Greensand, 6 m, and Gault, 50 m. The London clay is a relatively impermeable, overConsolidated clay, but the Lower London Tertiaries are represented by a series of sands, loams, and clays. In the central and eastern parts of the basin, the lower part of the Lower London Tertiaries is arenaceous. This facies, which has been referred to as the Basal Sands [Water Resources Board, 1972], attains a thickness of more than 30 m east of London and is commonly in hydraulic continuity with the Chalk. The Chalk is a soft, fine-grained limestone. Groundwater flow in the aquifer is predominantly through fissures, which are mainly in the upper 60 m and tend to be well developed along valleys, particularly in the unconfined areas but sometimes also in the confined area. The Chalk is underlain by the Upper Greensand and the Gault; the latter, being an argillaceous deposit, forms the base of the aquifer system. Much of the London Basin is drained by the River Thames. Groundwater flows from the outcrops on the northern and southern flanks of the basin through the confined part of the aquifer to natural discharge areas in the Thames valley. Since the eighteenth century, groundwater in the Chalk and the Lower London Tertiary sands has been developed for water supply. Groundwater levels have fallen in the center of the basin by as much as 70 m, and an increasing proportion of the natural discharge has been intercepted by pumped wells which are now the main outlet from the confined area, natural discharge no longer taking place from the central and eastern parts of the basin. The groundwater in the Chalk and Lower London Tertiary sands at outcrop is of the calcium bicarbonate type. Generally, this changes into a sodium bicarbonate type...

Tufa is a superficial, secondary deposit of calcium carbonate which accumulates on precipitation from emergent spring waters. It occurs as discrete, localized masses in regions of calcareous country rock.In the United Kingdom, deposits vary widely in structure and thickness but little is known of the rate of deposition. Some deposits contain laminae assumed to represent annual growth increments and which should contain a 14C and stable isotope record related to the original water from which it was precipitated.Investigations are reported on tufa from, three areas of different limestones in the United Kingdom (Northwest Yorkshire, South Derbyshire and North Oxfordshire).Hydrologically, the dating of tufa by 14C involves the same problems as the dating of groundwater. In the case of actively forming tufa, however, it is possible to derive a sequence of measurements, beginning with present day deposition, which clearly demonstrates the applications of age corrections.At Gordale Scar, Northwest Yorkshire, a profiling study of laminated tufa appears to show bomb trial 14C to a depth of 18mm below the surface, with almost constant values around 50 percent modern (raw data) from 18 to 48mm below the surface. The 14C content of surface tufa lies within the seasonal range of 14C measurements from the parent stream waters.Results of 50 percent modern in the sequence are consistent with the simplest correction procedures based on δ13C balance and the observed δ13C change on tufa precipitation is a practical demonstration of the fractionation factor ∊13. However, the application of corrections to active, surface tufa and parent waters collected monthly over a period of study (14 months) from all three sites, produce results higher than would be expected from published world 14C levels.