Investigation of Ancient Sites and Sources: Excavation Methods, Surveying Techniques Flashcards
Aerial Survey: Crop marks
Excavation Systems
Crops grow taller when growing over ancient ditches.
Crops do not grow as well over the remains of buildings.
From the air, these crop marks reveal outlines of ancient buildings.
Aerial Survey: Soil marks
Excavation Systems
Soil marks are visible after a field has been ploughed.
The soil is darker where ditches, pits, or mounds once stood.
These marks expose the outline of buried features like walls, buildings or entire settlements.
Aerial Survey: Shadow marks
Excavation Systems
When very low earthworks or mounds cast shadows, the outlines of sites can be revealed.
Open area excavation
Excavation Systems
Focuses on the site’s horizontal dimensions, uncovering the site layer by layer.
Each succeeding stratum is not exposed until the one above has been completely examined.
More commonly used than the grid method as it is less restrictive.
The grid system
Excavation Systems
Reveals the time sequence in the vertical layers exposed.
Surveyors divide the site into a grid of squares or boxes, marked out by string and numbered. They are excavated leaving a baulk in between grids.
The layers exposed (strata) are labelled.
When artefacts are uncovered, the coordinates of each grid record the location of the finds on a map of the site –> shows patterns of artefact distribution.
Satellite photography
Excavation Systems
Orbiting satellites take over 200 mapping photos using remote sensing technology, revealing the banks of old rivers, valleys and mountains.
Observation
Surveying Techniques
Taking notes of physical finds.
Concentration points of finds are good starting points for further excavation.
Geophysical survey: Ground-penetrating radar (GPR)
Surveying Techniques
An electromagnetic pulse radar signal is directed into the ground.
A receiver records the reflections from buried objects.
The time taken for the signal to reflect indicates the depth.
GPR is most useful when there are sandy soil condititons.
Geophysical survey: Resistivity surveying
Surveying Techniques
A resistivity meter passes an electric current between two metal probes in the ground to measure the resistance of the soil to the current.
Bured walls have a high resistance, while pits and ditches have low resistance.
Geophysical surveying: Magnetic surveying
Surveying Techniques
Magnetometer detects the magnetic properties of subsurface materials.
Highest readings come from iron, brick, burnt soil, rock.
Lower readings come from decayed organic materials.
