of the under-sluices is 4 feet higher than the river bed. There is thus ample allowance for a possible rise in the river bed. 2. =The Contour Map.=--The contour map, besides showing the contours of the country to be irrigated and of a strip of country, even if not to be irrigated, which will be traversed by the main line, should show all its main features, namely:--streams, drainages, railways, roads, embankments, reservoirs, towns, villages, habitations, and the boundaries of woods and cultivated lands. It should also show the highest water levels in all streams or existing canals. A map showing as many as possible of the above features should be obtained and lines of levels run for the contours. In doing this, the points where the lines of levels cut or pass near to any of the above features or boundary lines, should be noted. It may be necessary to correct inaccuracies in the plan or to supply defects in it. The greater the trouble taken to do this the less will be the trouble experienced later on. The heights of the contour lines will, in very flat country, have eventually to be only 1 foot apart. This will necessitate running lines of levels half-a-mile apart at the most, and preferably 2000 feet apart, the pegs in each line being about 500 feet apart. In less flat country the heights of the contour lines can be further apart than 1 foot. Whatever distance apart is decided on for them, the survey should be done once for all. On one of the Indian canals in flat country, the lines of levels were at first taken 5 miles apart, the branches roughly aligned and then further surveys made. This led to great expense and delay and the procedure has not been repeated. In making a contour survey, a base line, as centrally situated and as long as possible, should be laid down, with side lines parallel to it near the boundaries of the tract. The cross lines at half-mile or other intervals should then be laid down. Some of them may run out beyond the side lines. Circuits of levels should be run along the base line, the side lines and the two extreme cross lines and be carefully checked. The remaining cross lines should then be levelled. All the levels having been shown on the map the contours should be sketched in. The scale of the map for a large project may be two inches to a mile. If it is likely that the survey will have to be extended, it will be easier to do this by prolonging the base line and running more cross lines, than by prolonging each of the cross lines already surveyed. This can be borne in mind when selecting the base line.