Accounts of air reconnaissance in Britain have already been printed in this Journal (XLI, for north Britain; XLIII, for south Britain): the present paper records recent discoveries, bringing the previous records up to date.
Of the last five summers only in 1955 was there a marked drought favourable to the development of crop marks; but it has been possible to observe different parts of the country under a wide variety of conditions. These have allowed advantage to be taken of different combinations of weather, crops, and soil, so that a buried site invisible one year might be seen in another. Moreover, opportunities for reconnaissance in March and April have meant that large areas could be observed soon after spring ploughing, when soil-patterns in bare fields often reveal disturbances in the ground. These conditions have been particularly valuable for studying Celtic field-systems on the chalk downs and traces of ancient agriculture in the Fenland.
In the north, reconnaissance has revealed an interesting new group of military works, apparently of early date, at Troutbeck on the margin of the Lake District, besides yielding much fresh information at sites already known. This is particularly true of the extensive Roman sites in Scotland that often now lie within several different fields, not all of which are under suitable crops in any one year. Two forts, two signal-stations, and some sixteen temporary camps may be added to the list of discoveries given in JRS XLI.