The quantity of silt present at various depths can be found by pumping specimens of water through pipes. At each change of depth the pipe, delivery hose, etc., should be cleaned. Allowance must be made for the velocity of ascent of the water up the pipe. Suppose this to be 1·4 feet per second. Then the velocity of sand of class (·2) would be 1·2 feet per second, and the quantity of sand actually found in the water would have to be increased by one-sixth. 5. =Quantity and Distribution of Silt.=--The quantity of silt present in water varies enormously. Fine mud, even though sufficient to discolour the water, may be so small in volume that it only deposits when the water is still, and even then deposits slowly. In the river Tay, near Perth, the silt was found to be ordinarily 1/10,000 of the volume of water, and at low water only 1/28,000. In the river Sutlej at Rupar, near where it issues from the Himalayas, the silt in the flood season is extremely heavy. Out of 360 observations, made at various depths, during the flood seasons of four successive years, in water whose depth ranged up to 12 feet, the silt was once found to be 2·1 per cent. by weight of that of the water. It was more than 1·2 per cent. on four occasions, and more than 0·3 per cent. (or 3 in 1000) on sixty-four occasions. Generally about one-half of the silt was clay and sand of classes finer than (·10), about one-third was sand of class ·1/·2, and the residue was sand of class ·2/·3. The sand of the river Chenab is generally coarser than that of the Sutlej. There are very great differences in the degree of coarseness of river sand. The sand in any river becomes finer and finer as the gradient flattens in approaching the sea. Sea sand has been found to be of class (·20). In the Sirhind Canal, which takes out from the Sutlej at Rupar, the maximum quantity of suspended silt observed in the four flood seasons was 0·7 per cent., on one occasion out of 270, and it exceeded 0·3 per cent. on twenty-five occasions. About 80 per cent. of the silt was clay. In another part of the paper quoted, it is stated that the silt suspended in the canal water averaged, during the whole of one flood season, about 1/1700 of the volume of the water. This would be about 1/1200 by weight. The silt deposited in the bed of the canal, in a period of a few days, was sometimes as much as 1/1000 of the water which had passed along, and occasionally as much as 1/500. It was nearly all sand, only about 3 per cent. being clay. Silt of classes finer than (·1) gave no trouble, and were to be eliminated in future investigations. In a canal, as in a river, the sand on the bed becomes finer the further from the head.