BELOW Blackwall tunnel, which is thirty-five miles from the mouth of the Thames estuary, there are no facilities for crossing the Thames either by bridge or tunnel. The construction has now been approved of a tunnel, which will be called the Dartford-Purfleet tunnel and will connect the Purfleet-Grays Road on the north side of the river with the Dartford Southern by-pass, and a connexion will then be made with the London-Folkestone and the London-Hastings roads. As a first step (Roads and Road Construction, September 1), a pilot tunnel will be constructed 900 yards in length and with an internal diameter of 12 feet. Two ventilating shafts with diameters of 18 feet will be constructed on the Kent and Essex banks of the river. They will be approximately 100 feet in depth. The pilot tunnel will cost £300,000 and will provide information as to the strata under the river at this place. This will be very helpful in connexion with the construction of the main tunnel. The tunnel will be rather more than a mile in length. The cost of the whole scheme is estimated to be about three million pounds, the pilot tunnel costing about a tenth of this. The Ministry of Transport, which will be directly responsible for carrying out the work, has made, in conjunction with the county councils of Essex and Kent, all the necessary arrangements. This tunnel, which will be twelve miles down the river from the Blackwall tunnel, will form a much-needed link between the north and south sides of the Thames Estuary.