FORTH, river and firth of east Scotland. It is formed by two head streams, Duchray water and Avondhu, or Laggan as it is called after it leaves Loch Ard, both rising north-east of Ben Lomond in Stirlingshire, and uniting 1 m. west of Aberfoyle. From this point till it receives the Kelty, the Forth is in Perth shire, then it becomes the dividing line between Perth and Stirling as far as the confluence of the Allan. Thence it belongs to Stirling shire to a point II. m. due west of Cambus, whence it is the boundary between Stirling and Clackmannan. Owing to its tor tuous course between Gartmore and Alloa—the famous "links of the Forth,"—the actual length of the river is 66 m., or nearly double the distance in a direct line (3o m.) between the source of the Duchray and Kincardine, where the firth begins. The river drains an area of 645 sq.m. Its general direction is easterly with a trend towards the south. The alluvial plain from Gartmore to the county town is called the Carse of Stirling. The places of interest on the banks are Aberfoyle, Kippen, Stirling, Cambus kenneth, Alloa and Kincardine. The tide reaches 41 m. above Stirling, where the river is navigable at high water by vessels of tons. There is some shipping trade at Alloa.
The Firth of Forth extends from Kincardine to the North sea, a distance of 48 m. The width varies from 2 m. at Kincardine and I m. at Queensferry to 61 m. at Leith and 171 m. at the mouth. The principal ports on the south shore are Grangemouth, Bo'ness, Granton and Leith, and on the north, Burntisland and Kirkcaldy. Since the opening of the Forth bridge (see BRIDGES) in 1890 the ferries at Queensferry and Burntisland have greatly diminished in importance. The larger islands are Inchcolm, Inchkeith, with fortifications and a lighthouse, and the Isle of May, with a light house and a ruined chapel. The anchorage of St. Margaret's Hope, with the naval base of Rosyth, lies off the shore of Fife immedi ately to the west of the Forth bridge.