On some of the affluents of these rivers, which, under legislative powers granted last century, had been converted into “navigations,” the proprietors have obtained Acts of Parliament relieving them of their rights and liabilities, and there is now no jurisdiction over these rivers, or anybody responsible for removing shoals or cutting weeds. The beds of these streams have consequently become shallow, and they are no longer capable of acting as efficient arterial drains. Thus, on the Ivel, an affluent of the Ouse, the navigation trust, created in the reign of George II., was abolished in 1876. The river is said to have since diminished one-half in width, and one-half in depth, and the bottom is being gradually raised to the level of the land. In like manner, the Lark, another canalised affluent, has almost entirely silted up since the navigation of the river ceased. The Ouse itself, above Earith, is obstructed by numerous shoals, and an enormous growth of weeds. These were originally kept down by the constant passage of the vessels, and the shoals were removed by the trustees of the navigation. THE TEES. The improvements that have been carried out for the purpose of opening up the navigation of the river Tees, although less considerable than those carried out for some of the larger rivers of Great Britain, are yet entitled to take rank as among the most notable river engineering achievements of the century. They are also among the most recent. It was not until 1852 that the Act was passed creating the Tees Navigation Commission. At that time there were three or four channels in the estuary, all of them very shallow. The shifting sandbanks caused great trouble and not a little danger to navigation, and the depth of water near to Middlesbro’ did not admit of the passage of vessels of large size. Since then, about twenty miles of low water training walls have been erected for the purpose of confining the navigable channel. The volume of water and its scour have thereby been much increased. The river has been continuously dredged in order to secure a depth of water that would allow of the passage of vessels of large tonnage into the Middlesbro’ Docks. About 23 million tons of material have been dredged from the bed of the river, and the channel has been generally straightened and widened. Breakwaters have been constructed on both sides, one of them, called the North Gare, being about two miles and a half long. A remarkable feature of the work is that these breakwaters have been constructed of slag, obtained from the blast-furnaces in the neighbourhood. Some millions of tons of slag have been employed in this way, the ironmasters having paid to the Conservancy Commissioners a small sum for removing the slag, the disposal of which had been a great source of difficulty previous to this application.