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Would YOU date radiocarbon?
How can you tell what is under the ground, without digging it up?
This page tells you a bit about the archaeological methods used to discover more about the history of Chichester Harbour.
Archaeologists like to find out as much as possible about evidence which is buried under the ground before they start digging at all! You can probably guess why this is. The main reason is to avoid damaging important evidence.
Can you think of any other reasons for trying to find out as much as possible about a site first? What about cost, or looking silly for digging in the wrong place?
So archaeologists often begin by looking at paper evidence. You could look at maps, letters or other historical documents.
Even if the site is pre-historic (before written history), it may be shown on a map. Place names can give clues to the location of ancient remains.
This will help you identify a promising site, or place of special archaeological interest.
Talking to local people can also be useful. Oral history is spoken history. It could be information about a place that local people have always talked about, or it could be aneyewitness account, such as accounts of life during World War 2.
If you are rich enough to have a helicopter, you could look for markings from the air! If you go up when the weather has been dry, you could look for parch Marks. If there is stone under the ground, an old wall, for instance, the grass on top of it will look dry (there isn't much soil to hold water).
An old ditch will show up as a darker green line (as there is more soil to hold water for the grass). Crops like corn grow taller over ditches; tall areas of crops can cast shadows, showing up shapes of ditches below the soil.
In some places you can make out the walls of whole buildings by this method. In fact you can even do this from the ground, but it is harder to see large shapes.
Field walking has been done in the Harbour area. A group of people walk across a field, or along the shore, picking up anything that looks old and man-made. They note where in the field the "finds" come from. If there are many finds, that may lead to further investigations!
If you can get hold of special equipment, you might now do a geophysical survey.
Magnetometers were used at Copperas Point to find the Roman kiln where roof tiles were fired. Magnetometers measure magnetic traces in the soil, with higher readings where something has been burnt. A trench was dug in August 2007 which confirmed the location of the kiln.
In the harbour seismic refraction has been used at Copperas Point,south of Dell Quay, to find a possible clay pit. This fits with the traces of Roman tile making in the area. Seismic refraction sends seismic energy through the ground and measures different types of rocks and soils below. A geo-electricalsurvey measures how easily electrical energy can pass through the ground, showing the different types of rocks and soil below. You can then use this information to understand the geology of the area, or spot ancient channels, such as at Horsepond.
By now you might be getting pretty excited about what lies below the ground at your site. Maybe what you have found is now judged to betoo important to dig up! This is good and bad. It means that your research will be recorded, and the site will be saved undamaged for future study, using even better techniques. On the other hand, you may never know what is really there and what it might tell us about the past.
If you get the go-ahead for further study, you could now dig a small test pit to try to confirm your ideas of what is underground.
Or you might use an auger. In Chichester Harbour augers have been used to twist into the ground and pull out a sample of earth to look at. The deeper down you go, the further back in time you can investigate. Auger samples taken in Fishbourne Channel showed that there are thin layers of silt and gravel above bedrock, and that the channel would have been too shallow for large Roman boats.
In Chichester Harbour, cores have been taken in seven places. A long tube of earth and rock is pulled out of the ground and carefully cut open.
It is looked at in great detail. Fossils, different types of earth and rocks can tell us about the harbour in the past, for example, sea shell fossils mean that the area was underwater. Pollen and seed from plants are radiocarbondated so that we can see the types of plants growing at different times. Radiocarbon dating can tell us how long ago something died, so we can work out the age of things that used to be alive, within the last 50,000 years or so.
To find out more about what coring and pollen analysis tell us about Chichester Harbour, go to the Harbour Landscape Timeline.
Sometimes trenches are dug in the ground so that archaeologists can look at what is there. Trenches were used a lot in the past, when survey methods weren't as clever.
When you dig a trench, you go slowly and carefully, layer by layer, recording finds and soil features as you go. Often a trench has been dug for other reasons, such as laying new pipes at Fishbourne.
An archaeologist is called in to see what is there, and to make sure that important areas are saved, and information recorded. This is sometimes called "Rescue Archaeology".