it--supposing the features of the country admit of this--will be desirable. It may increase the length of distributaries taken off near the bends. It will be shown (CHAP. II. Art. 10) that a distributary ought, when matters can be so arranged, to irrigate the country for two miles on either side of it, and watercourses should be two or three miles long. A distributary need not therefore extend right up to the boundary of the commanded area but stop two or three miles from it. Generally it is not desirable to prolong a distributary and make it “tail” into another channel (CHAP. II. Art. 3). A distributary, like a canal, may give off branches. None of the rules mentioned in the preceding paragraph are intended to be other than general guides, to be followed as far as the physical features of the country permit, or to assist in deciding between alternative schemes. It may for instance be a question whether to construct one distributary or two, between two nearly parallel branches. The two-mile rule may enable the matter to be decided or it may influence the decision arrived at as to the exact alignments of the branches. The flatter the country and the less marked the ridges the more the alignment can be based on the above rules. Sometimes, as in the low land adjoining a river, the ridges are ill defined or non-existent and the alignment is based entirely on the above rules. The rule as to following high ground need not be adhered to at the tail of any distributary if all the land to be irrigated at the tail is low and if there is a deep drainage line or other feature of the country such as to preclude the possibility of an extension of the distributary. Possible extensions should always be considered. In hilly districts an irrigation canal may have to run in sidelong ground along the side of a valley. In flat valleys, owing to the land nearest the river having received successive deposits of silt in floods, the ground generally slopes away from the river and a canal can irrigate the low land even if taken off at right angles to the river. But to irrigate the high land near the river and the land where it rises again towards the hills or watershed, a canal taking off higher up the river is necessary. Of course much depends on whether the canal is to irrigate when the river is low or only when it is high, and whether or not there is to be a weir in the river. In Upper Egypt, it is common for a high level canal taking off far upstream, to divide into two branches, one for the land near the river and one for the land towards the watershed, and for both branches to be crossed--by means of syphons--by a low-level canal which irrigates the low ground. Similar arrangements sometimes occur on Indian inundation canals.