The Highland Line may be said at its southern end to commence at Loch Lomond, in the earldom of Lennox, where the Pass of Balmaha between the lake and the commencement of the mountain region leads into the district of which this lake is the centre. The line then enters the earldom of Menteith, and crosses the Forth, here called the _Avon dubh_, at Aberfoil, and proceeds from thence to Callander, where the pass on the north side of Loch Vennachar leads into the district formerly called Strathgartney, and the Pass of Leny forms the entrance to Strathire and to the district of Balquhidder. From Callander the line follows the range of the Grampians, through the earldom of Stratherne, and crosses the river Earn at Crieff, and the Almond at Findoch, where passes lead to the upper part of the Vale of the Earn and to Glenalmond respectively. From thence it follows the line of the Grampians to Dunkeld, where the King’s Pass forms the entrance to Strathtay, and through the district of Stormont in Gowry to Blairgowrie, where the passes lead into the district of Strathardell. From thence it follows the line of the Grampians till it crosses the Isla north-west of Alyth, and enters the earldom of Angus, where the minor range of hills forming the east side of Glenisla coincides with the line till it reaches the great chain of the Mounth, or backbone of the Grampians, at Cairn Bannoch. There it enters the earldom of Mar, and proceeds along the west side of Glenmuich to the Dee at Ballater, where the Pass of Ballater leads into the districts of Strathdee and the Forest of Braemar. North of these districts it includes likewise the district of Strathdon, crossing the river Don at Boat of Forbes, whence it proceeds to the river Spey at Craigellachie, including the district of Strathavon, and here a pass leads into the district of Strathspey, and separating the mountain region of the earldom of Moray from the level plains forming the southern seaboard of the Moray Firth, it terminates at the mouth of the river Nairn, which flows through the town of Nairn, and formerly separated the Gaelic-speaking people on its left bank from the lowland population on the right. The Highland Line thus intersects the old earldoms of Lennox, Menteith, Stratherne, Gowry, Angus, Mar, Buchan, and Moray, which represented the older great Celtic tribes or _Mortuath_, governed by their _Ri Mortuath_ or _Mormaers_, and the portion of each earldom included in the Highland Line consisted of that part which retained its Gaelic population intact, while the rest of it became more or less colonised by foreign settlers. [Sidenote: Break-up of the Celtic earldoms.]