The detail levelling is carried out contemporaneously with the progress of the cadastral survey. Starting from the marks on the initial series, lines are run along nearly all the turnpikes and parish roads, and bench marks cut at intervals of about a quarter of a mile. The whole of the bench marks of the initial levelling are shown in position on the 25-inch manuscript plans, and their heights given to the nearest tenth of a foot. Surface heights, to the nearest foot are also marked on the plans, at frequent intervals between the bench marks. CONTOURING. Contrary to the custom in other countries, the contours of the English survey have all been surveyed and levelled on the ground, checked by the numerous bench marks, the standard of accuracy demanded in levelling being two-tenths of a foot. Owing to the expense of the process, about $1.25 per lineal mile, only the 100 foot contours have been surveyed, except where greater detail is required for military purposes, which information is not furnished to the public. HILL SHADING. The hill features for the one inch maps are first sketched in the field by the military method of slopes and sketch contours or proof impressions of the contoured sheet. Finished drawings from the field sketches are then made on cardboard impressions from the one inch outline plates, and finished as guides for the engraver to work by. Beautiful and delicate in finish as is all the work of the copperplate engravers on the Ordnance Survey, there is perhaps no branch in which they so peculiarly excel as in their delineation of hills on the one inch maps. III. It is impossible in the limits of a single paper to attempt to describe the methods and processes of publication which are carried at the headquarters of the Ordnance Survey at Southampton. Carefully prepared treatises on the subject have been written by officers engaged in the work, and for clear and concise description none are better than the series of articles by Captain H. Sankey, R. E., published in _Engineering_, in 1888. There are two points of great interest in connection with the Ordnance Survey which cannot be neglected. The one its military organization, and the other the economy of its methods of publication. Of its military organization, which has continued since the first surveys were made for military purposes, it may be said that the conservative precision of its methods of field work are best adapted for military control and discipline. Under the successive superintendence of highly educated officers of the Royal Engineer Corps, whose patriotic efforts have been to secure efficiency and economy in the service, the country has greatly profited. Many of the improvements and inventions that have made possible the publication of maps of all scales at the lowest possible cost, are the results of experiments made by these officers.