For some years past observation has been made and photographs taken from the air of the marks which appear in the crops near Dorchester and it is now possible to give a fairly complete survey of them.
These marks, the appearance of which is dependent on the suitability of the crop and weather conditions. appear generally as lines, rings or dots of a darker green in the crops and are due to ancient disturbance of the subsoil. If at some time a ditch or pit penetrating the subsoil has been dug in a field and later has been levelled, the filling will be of a different nature to the soil it replaces and have a beneficial effect on that part of the crop which grows directly over it. By means of these marks the position of buried works can he located. Attention was first drawn to crop marks near Dorchester by the discovery by two officers of the Royal Air Force of the great rings to the north of the village. At the same time marks were seen on and near the Minchin Recreation Ground and on Bishop's Court Farm.
Since 1933 I have watched this area in all seasons of the year and have taken many photographs of it from the air. From year to year as crop conditions changed more marks have been visible in the same field as the great rings. Several small circles lie at the northern end of this field, three of them with interrupted ditches, apparently similar to those discovered in then Neolithic settlement at Abingdon. Near the Dorchester-Abingdon Road there is a small square enclosure which apparently contained a round barrow, and there is a slight mound on the ground at this spot. A similar square enclosure on Limlow Hill, Litlington. Cambs., contained a round barrow. Other circles, apparently showing the ditches of levelled round harrows lie near the great rings, one inside their annulus, and two small square enclosures lie a little farther to the south. The great rings themselves are not truly circular and each has two entrances, one towards the north and one towards the south. The purpose of the nearly straight parallel lines which pass to the east of the great rings is as yet unexplained. Several other similar pairs of lines, some forming square ended enclosures, have been found within a few miles of Dorchester.
These lines are continuous so far as it has been possible to trace them, with the exception of a small break towards the northern end of the field and a wider break farther south. This latter gap is partly filled by a double circle.
The rectangular enclosure at Benson has a similar break, and the same type of enclosure at Sutton Courtenay has one of the lines crossing a circle, but no break appears in the lines.
In the other examples these enclosures have been seen to have square ends to the parallel lines, but at Dorchester it has not been possible to trace their extremities. Their extension to the North West is covered by a grass field and as grass does not readily produce crop-marks no signs of them can be seen in that direction. In a south-easterly direction they extend into a field near Queensford mill and appear to end there, but a rather mixed collection of other lines occurs and confuses the issue. It may be found possible to trace them further in this direction. If they did so extend they would lead to a point on the Thame from which another pair of parallel lines leads towards a large enclosure near Warborough. The junction of this second pair with the enclosure was obscured by ploughing when this photograph was taken, and only a portion of one side of the enclosure appears in the lower right hand corner of the photograph.
The lines are truly straight and parallel but more closely spaced than those associated with the great rings. Although they lead direct to the enclosure and have been traced no farther, there is no break in the enclosure at the point of contact. There is, however, an entrance to the enclosure towards its south-east corner.
The double circle within the enclosure is apparently the site of a round barrow which has been almost entirely levelled. Its outer ring is approximately 100 ft. in diameter and l0 ft. wide. Westwards of this can be seen a triple circle with a wide outer ring within which there is a broken ring of dots, then a smaller continuous circle and centrally a dot. This does not seem to show the site of any of the common types of round barrow and, whilst it may be rash to anticipate the results to be obtained from excavation, one may make the suggestion that these marks may show the site of a timber circle.
Leading from it towards the Thame is a right-angled line, probably evidence of a ditch which drained the outer circular ditch. Close by there is an elongated D-shaped enclosure which has a marked resemblance to another found in Allen's gravel-pit to the north of Dorchester, in the ditches of which were found quantities of Iron Age pottery.
The circle to the south of the `timber circle' is probably that of a round barrow and the disturbed area in which it lies may show the activities of gravel-diggers in fairly recent times. Other cases have been noted at Radley and Langford near Lechlade, where the digging of gravel has ceased when the ditch of a barrow has been encountered. The diggers finding the increased depth of topsoil and being unaware that this extra depth of overburden is only of narrow extent, cease digging in that direction and thus the remains of barrows are saved from destruction. Another small square, similar to those near the great rings, lies near the parallel lines. The area between the Dyke Hills and the Thames is a mass of marks. There are several bold enclosures with fairly straight sides, other less well-defined straight-sided enclosures, many circles both continuous and with gaps, and a multitude of dots. These marks seem to be characteristic of an lron Age settlement of considerable extent and density of population, but from the way in which the marks are intermixed they would seem to indicate works extending over a considerable period of time. Apart from two small circles near the Thame and a single squarish enclosure to the south-west of Dorchester one other site remains, the large rectangular enclosure, with a small rectangle within it, which lies close to a bend of the Thame. This would seem to be of later date than the other marks since a stone coffin was found thereabouts.
Thus far can air-photography carry us; further photographs in future years may help to clear up, or increase, the problems already presented, but the ultimate solution rests with those on the ground. There can be few areas which present such a wealth of early remains of a variety to suit the tastes of archaeologists no matter what period they may favour.