Investigation of Ancient Sites and Sources: Excavation Methods, Surveying Techniques Flashcards
Excavation Systems
Aerial Survey: Crop marks
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.
Excavation Systems
Aerial Survey: Soil marks
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.
Excavation Systems
Aerial Survey: Shadow marks
When very low earthworks or mounds cast shadows, the outlines of sites can be revealed.
Excavation Systems
Open area excavation
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.
Excavation Systems
The grid system
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.
Excavation Systems
Satellite photography
Orbiting satellites take over 200 mapping photos using remote sensing technology, revealing the banks of old rivers, valleys and mountains.
Surveying Techniques
Observation
Taking notes of physical finds.
Concentration points of finds are good starting points for further excavation.
Surveying Techniques
Geophysical survey: Ground-penetrating radar (GPR)
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.
Surveying Techniques
Geophysical survey: Resistivity surveying
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.
Surveying Techniques
Geophysical surveying: Magnetic surveying
Magnetometer detects the magnetic properties of subsurface materials.
Highest readings come from iron, brick, burnt soil, rock.
Lower readings come from decayed organic materials.
