a river of England, is formed by the union of several small streams which take their rise in the hills near the borders of Yorkshire, Cheshire, and Derbyshire, where these three counties meet in a single point. The principal of these streams are the Tame and the Goyt; and from Stockport, where these two unite, the river thus formed takes the name of the Mersey, flows to the W., forming all along its course the boundary between Cheshire and Lancashire, and after a course from Stockport of 55 miles in length, falls into the Irish Sea below Liverpool. The principal tributaries of the Mersey are—the Irwell, which flows past Manchester, and falls into the Mersey from the N., below the junction of which the river becomes navigable; and the Weaver, which joins it from the S. just before it expands into a large estuary. This estuary, which is 17 miles in length and 3 miles across at the broadest part, contracts at its mouth to a breadth of little more than three-quarters of a mile, so as to have the appearance, from several points of view, of a large inland lake. The country through which the Mersey flows is level; but in some parts the scenery is very picturesque. The principal towns and villages on its banks are—Stretford, Warrington, Hale, Garston, and Liverpool, on the right bank; and Stockport, Runcorn, Ince, and Birkenhead, on the left.

MERTHYR TYDVIL or TYDVL, a parliamentary borough and market-town of South Wales, Glamorganshire, situated on the Taff, 22 miles N. by W. of Cardiff, and 171 W. by N. of London. The town, although it is said to be named after an ancient British martyr of the name of Tydvil, is entirely of modern origin, and consists chiefly of the cottages of workmen, meanly and irregularly built. Of late, however, the town has been much improved, and it now contains some regular and well-built streets, a court-house, a market-house, several elegant private residences, and a large number of excellent shops. The town contained in 1851 no fewer than 84 places of worship belonging to the following denominations—Independents, 20; Baptists, 19; Church of England, 10; Wesleyan Methodists, 10; Welsh Calvinist Methodists, 10; Unitarians, 2; Primitive Methodists, 2; Wesleyan Reformers, 2; isolated congregation, 1; Roman Catholics, 1; Latter-day Saints, 6; Jews, 1. There were also at that time 68 Sunday schools, 16 public and 43 private day schools. The town has a library and reading-room, as well as several book-clubs—all which facts afford evidence of the progress which the inhabitants are making in education and intelligence. Merthyr Tydvil, situated in a bleak and barren country, was at an early period known as a place for the smelting of iron ore, but it was never carried on to any great extent till Mr Anthony Bacon in 1755 obtained a lease of a district of land, 8 miles in length by 5 in breadth; and from that time may be dated the rise of the prosperity and importance of the town. Having erected extensive ironworks, and made a contract with the government for supplying the arsenals with cannons, he acquired an immense fortune, and finally disposed of the land in smaller portions to other individuals. From that time the works have gone on increasing in extent and in prosperity; and it is not difficult to account for the rapid rise of a large town in the vicinity, seeing that from 4000 to 5000 hands are employed in one establishment alone, and that upwards of £1,000,000 is paid annually as wages in the four large ironworks in the district. There are now nearly fifty blast-furnaces in the vicinity of the town, producing annually from 150,000 to 200,000 tons of iron, which are for the most part conveyed by railway or canal to Cardiff, whence they are shipped to their various destinations. In the vicinity of Merthyr Tydvil there are numerous country seats, belonging principally to the wealthy proprietors of the different ironworks. Since the passing of the Reform Bill Merthyr Tydvil has returned one member to the House of Commons. The market-day is Saturday; and there are three annual fairs. Pop. (1851) of the borough, including the town of Dowlais, 63,080.