THE Wandle-Valley Main Drainage Works, recently completed for the Croydon Rural Sanitary authority, embraces the construction of about 50 miles of main sewers, with the necessary outfall works, for the collection and disposal of the sewage of the parishes of Mitcham, Beddington, Merton, Morden, Wallington, and the special drainage district of Merton Rush, Surrey. The area of the combined district is 10,106 acres, and the present population about seventeen thousand. About one-fourth of the area is within the watershed of the Beverley brook, and the remainder in that of the River Wandle. The relative levels of the northernmoet part of the district being lower in the Wandle watershed, and, in consequence of the more rapid fall of the valley, the flooding being less serious than in the valley of the Beverley brook, it follows that in a combined system of sewers, the most economical plan to adopt would be that in which the outfall-works were situated in the first-named valley, other considerations in reference to the disposal of the sewage being equally favourable ; as, however, much diffic d t y was experienced in procuring land suitable for sewage S sposal in the Wandle valley, in the early schemes prepared, one by Sir Joseph Bazalgette, C.B., President Inst. C.E., and one by Mr. Baldwin Latham, M. Inst. C.E., the outfall-works were situated in the Beverley brook valley.As regards the physical character of the district, that part of it situated in the watershed of the Beverley brook is flat, and consists of London clay. The Wandle valley, on the other hand, has a comparatively steep fall, as attested by the numerous mills using the water power of the Wandle, and the geological features vary extremely. The watershed is a very large one, extending as far as Caterham on the south, Norwood on the east, and Sutton on the west ; the chalk area alone exceeding 60 square miles. The Wandle derives its water from this large chalk area, and flows down the valley from its sources at Carshalton, Beddington, and Croydon, over beds of alluvium lying on the London clay. Various animal remains were found in the cuttings for the sewer in this alluvium, among them the tusks and teeth of an elephant.