Forfarshire is characterized by great variety of surface and may be divided physically into four well-marked sections. In the most northerly of these many of the rugged masses of the Grampians are found; this belt is succeeded by Strathmore, or the Howe of Angus, a fertile valley, from 6 to 8 m. broad, which is a continuation of the Howe of the Mearns, and runs south-westwards till it enters Strathearn, to the south-west of Perth; then come the Sidlaw Hills and a number of isolated heights, which in turn give way to the plain of the coast and the Firth. The mountains are all in the northern division and belong to the Binchinnin group (sometimes rather inexactly called the Braes of Angus) of the Grampian ranges. Among the highest masses, most of which lie on or near the confines of the bordering counties, are Glas Maol(3502 ft.), on the summit of which the shires of Aberdeen, Forfar and Perth meet, Cairn-na-Glasha (3484), Fafernie (3274), Broad Cairn (3268), Creag Leacach (3238), Tolmount (3143), Tom Buidhe (3140), Driesh (3105), Mount Keen (3077) and Mayar (3043), while peaks of upwards of 2000 ft. are numerous. The Sidlaw Hills--the greater part of which, however, belongs to Perthshire--are much less lofty and of less striking appearance. They have a breadth of from 3 to 6 m., the highest points within the county being Craigowl Hill (1493 ft.), Auchterhouse Hill (1399) and Gallow Hill (1242). None of the rivers is navigable, and only three are of any importance. The Isla, rising in Cairn-na-Glasha, flows southwards, then turns S.E. and finally S.W. till it enters the Tay after a course of 45 m. Its chief tributaries on the right are the Alyth, Ericht and Lunan, and on the left the Newton, Melgam and Dean. Near Bridge of Craig is the fall of Reekie Linn (70 ft.), so named from the fact that when the stream is in flood the spray rises in a dense cloud like smoke (_reek_). Near old Airlie Castle are the cascades called the Slugs of Auchrannie. The North Esk, formed by the confluence of the Lee and Mark at Invermark, after a south-easterly course of 28 m. enters the North Sea 3 m. N. of Montrose. On the right bank it receives the West Water and Cruick and on the left the Tarf and Luther. It gives the title of earl of Northesk to a branch of the Carnegie family. The South Esk rises in the Grampians near Mount Fafernie and not far from its source forms the Falls of Bachnagairn; after flowing towards the south-east, it bends eastwards near Tannadice and reaches the North Sea at Montrose, the length of its course being 48 m. Its principal affluents are the Prosen on the right and the Noran on the left. It supplies the title of earl of Southesk to another branch of the Carnegies. The lakes are small, the two largest being the Loch of Forfar and the mountain-girt Loch Lee (1 m. long by 1/4 m. wide). Lintrathen (circular in shape and about 3/4 m. across), to the north of Airlie Castle, supplies Dundee with drinking water.