Forth, a river and estuary of Scotland, formed by the junction of the Duchray and the Dhu, rising in Stirlingshire and Perthshire respectively. The junction is at Aberfoyle - of Nicol Jarvie fame - and after forming the boundary for some distance between Stirlingshire and Perthshire, the river opens out into a broad firth reaching the German Ocean after a course of 170 miles. It flows through a rich country, and through the Links of Forth it winds greatly, the distance between Stirling Bridge and Alloa being 6 miles by land and 12 by water. One of the peculiar features of the river is a curious double tide. The Forth Bridge [Bridge] is one of the greatest engineering triumphs of our day. The river has good salmon, and the estuary has white fish, herrings, and oysters. The Firth narrows at Queen's Ferry - named after Margaret, wife of Malcolm Canmore - and this is supposed, from the Roman remains in the neighbourhood, to have been the Roman "Freti transitus." In mid-channel is Inchgarvie, on which are the ruins of a 16th century castle erected to protect the shipping in St. Margaret's Hope just west of the Ferry, which is the greatest natural harbour for refuge on the east coast of Scotland. In the Civil War a Captain Roy blew up the magazine to keep it out of Cromwell's hands, and in 1779 it was put in repair on account of Paul Jones's raids on the coast. The river is only about a mile across at the ferry, and the Inch reduces the passage on each side to less than 600 yards. There are two lighthouses. The river receives several tributaries.