The difficulty of dating landscapes
It is difficult to date cropmark landscapes without finding objects from specific periods or material suitable for scientific dating either by surface collection or excavation. The ones photographed by Riley were clearly very old, but how long they had been buried was something of a mystery until he observed that the line of a Roman road cut through some of the fields. The fields must have been earlier than the road.
Based on the photographs taken by Riley and others, archaeological excavations have been recommended by South Yorkshire Archaeology Service whenever aggregates extraction has been planned in areas where cropmarks have been recorded. The resulting work has told us much about ancient Doncaster. Objects found by excavation give an approximate date for when a ditch was filled in. Roman pottery and other artefacts have been found in many of the filled-in ditches, but often near the top, which suggests that the ditches themselves were dug some time earlier. Rare finds of Iron Age pottery suggest that the fields originated in the centuries before the Romans arrived but stayed in use throughout the Roman period.
Ways of surveying
Geophysics is a way of surveying buried features without disturbing the ground surface. One method measures the magnetic characteristics of the soil. These can be altered by such actions as digging ditches and pits or heating the ground surface below hearths and kilns. The magnetic traces of these activities can survive for thousands of years. A plan of magnetic responses can be drawn by a computer to show where there are probable archaeological features. [Geophysicists use a computer to draw a plan of magnetic responses to show buried features]
Archaeologists can locate and partly date buried features by fieldwalking on ploughed fields. Objects turned up by the plough are systematically collected and plotted on a map. Concentrations of finds are likely to indicate buried features. Dating the finds will indicate when those features were in use.
For further information, please contact us:
- tel: 0114 273 6354
- address: South Yorkshire Archaeology Service, Howden House, 1 Union Street, Sheffield, S1 2SH