Cropmark
Encyclopedia
- See crop markCrop markCrop mark may refer to*in printing, marks placed at the corners of a form to indicate where the page is to be trimmed*Cropmarks, in archaeology: differential growth indicating buried sites*Crop circles...
for disambiguation.
Cropmarks or Crop marks are a means through which sub-surface archaeological, natural and recent features may be visible from the air
Aerial archaeology
Aerial archaeology is the study of archaeological remains by examining them from altitude.The advantages of gaining a good aerial view of the ground had been long appreciated by archaeologists as a high viewpoint permits a better appreciation of fine details and their relationships within the wider...
or a vantage point on higher ground or a temporary platform. Along with soil mark
Soil mark
Soil marks are differences in soil colour as a result of archaeological features. They can be seen when a ploughed out earthwork has left hard dry material of a former bank and damper wetter material from a former ditch. They can also occur when a feature has cut through the top soil to reveal...
s and frost marks they can reveal buried archaeological sites not visible from the ground.
Description
Crop marks appear due to the principle of differential growth. One of the factors controlling the growth of vegetation is the condition of the soil. A buried stone wallStone wall
Stone walls are a kind of masonry construction which have been made for thousands of years. First they were constructed by farmers and primitive people by piling loose field stones in what is called a dry stone wall, then later with the use of mortar and plaster especially in the construction of...
for example will affect crop growth above it, as its presence channels water away from its area and occupies the space of the more fertile soil. Conversely, a buried ditch
Ditch
A ditch is usually defined as a small to moderate depression created to channel water.In Anglo-Saxon, the word dïc already existed and was pronounced 'deek' in northern England and 'deetch' in the south. The origins of the word lie in digging a trench and forming the upcast soil into a bank...
, with a fill containing more organic matter than the natural earth, provides much more conducive conditions and water will naturally collect there, nourishing the plants growing above.
The differences in conditions will cause some plants to grow more strongly and therefore taller, and others less strongly and therefore shorter. Some species will also react through differential ripening of their fruits or their overall colour.
Particularly effective crops that exhibit differential growth well include cereal
Cereal
Cereals are grasses cultivated for the edible components of their grain , composed of the endosperm, germ, and bran...
crops, pea
Pea
A pea is most commonly the small spherical seed or the seed-pod of the pod fruit Pisum sativum. Each pod contains several peas. Peapods are botanically a fruit, since they contain seeds developed from the ovary of a flower. However, peas are considered to be a vegetable in cooking...
s, and potato
Potato
The potato is a starchy, tuberous crop from the perennial Solanum tuberosum of the Solanaceae family . The word potato may refer to the plant itself as well as the edible tuber. In the region of the Andes, there are some other closely related cultivated potato species...
es.
Differential growth will naturally follow any features buried below. Although the growth differences may appear small close up, from the air the pattern they make is more visible as the small changes can be seen in the context of the normally growing surrounding vegetation as differences in tone or colour. When the sun is low to the horizon, shadows cast by the taller crops can also become visible.
By their nature crop marks are only visible seasonally and may not be visible at all except in exceptionally wet or dry years. Drought
Drought
A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...
s can be especially useful to cropmark hunters as the differential growth can become apparent in normally hardy species such as grass. The drought of 2010 produced particularly good conditions for observing crop marks in the UK.
The usefulness of cropmarks to archaeologists has largely been a fruit of inspection from aircraft, but the possibility was suggested by Rev. Gilbert White
Gilbert White
Gilbert White FRS was a pioneering English naturalist and ornithologist.-Life:White was born in his grandfather's vicarage at Selborne in Hampshire. He was educated at the Holy Ghost School and by a private tutor in Basingstoke before going to Oriel College, Oxford...
in The Natural History of Selborne (1789), in a note appended to his Letter VI, to Thomas Pennant, apropos of local people's success in searching for bog oak for house construction, by discovering these trees "by the hoar frost, which lay longer over the space where they were concealed, than on the surrounding morass. To White it suggested the query "might not such observations be reduced to domestic use, by promoting the discovery of old obliterated drains and wells about houses; and in Roman stations and camps lead to the finding of pavements, baths and graves, and other hidden relics of curious antiquity?"
Examples
Examples of archaeological sites where cropmarks have been observed are BalbridieBalbridie
Balbridie is the site of a Neolithic timberhouse in Aberdeenshire, Scotland, situated in the south Deeside near the B9077 road. This archaeological site is one of the earliest known permanent neolithic settlements in Scotland, dating to 3400 to 4000 BC...
and Fetteresso
Fetteresso Castle
Fetteresso Castle is a 14th century towerhouse, rebuilt in 1761 as a Scottish gothic style Palladian manor, with clear evidence of prehistoric use of the site. It is situated immediately west of the town of Stonehaven in Kincardineshire slightly to the west of the A90 dual carriageway...
in Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
.
In 2009, investigation of crop marks near Stonehenge
Stonehenge
Stonehenge is a prehistoric monument located in the English county of Wiltshire, about west of Amesbury and north of Salisbury. One of the most famous sites in the world, Stonehenge is composed of a circular setting of large standing stones set within earthworks...
revealed a variety of 6,000 year old prehistoric subterranean structures.
Another example is the rediscovery of Altinum
Altinum
260px|thumb|Remains of the Roman [[decumanus]].Altinum is the name of an ancient coastal town of the Veneti 15 km SE of the modern Treviso, northern Italy, on the edge of the lagoons...
, a precursor to the city of Venice
Venice
Venice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...
, from a combination of visible and near-infrared photos of the area taken during a drought in 2007.
The multi period site at Mucking
Mucking excavation
The Mucking excavation was a major archeological dig that covered an area of near Mucking, in southern Essex, England. The excavations took place between 1965 and 1978, prior to gravel extraction. At the time it was the largest excavation in Europe and it was the first opportunity to excavate a...
was discovered as a result of aerial photographs showing cropmarks and soil mark
Soil mark
Soil marks are differences in soil colour as a result of archaeological features. They can be seen when a ploughed out earthwork has left hard dry material of a former bank and damper wetter material from a former ditch. They can also occur when a feature has cut through the top soil to reveal...
s. The earliest photographs to reveal the site were taken by the Luftwaffe
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....
in 1943. The importance of the site was recognised following photographs taken by Dr JK St. Joseph
Kenneth St Joseph
John Kenneth Sinclair St Joseph, CBE was a British archaeologist, geologist and Royal Air Force veteran who pioneered the use of aerial photography as a method of archaeological research in Britain and Ireland.-Early life:...
in 1959 (published in 1964). In 1982, Margaret Jones (site director at the Mucking excavation) noted that some sites were being interpreted on crop mark evidence alone. She pointed out that some features do not produce crop marks and that some crop marks, when excavated, turn out not to be what they seem.