It lies in the upper part of the Ribble valley, amid the wild scenery of the limestone hills of the Pennine system.
More important are the rivers that descend from the main chain of the Graian and Pennine Alps and join the Po on its left bank.
The principal structural feature is the broad anticline, its axis running north and south, which has brought up the Carboniferous Limestone; this uplifted region is the southern extremity of the Pennine Range.
To the north, west and south, a flat coastal belt, bordering the Irish Sea, with its inlets Morecambe Bay and Solway Firth, and broadest in the north, marks off the Lake District, while to the east the valleys of the Eden and the Lune divide it from the Pennine mountain system.
Forbes was also interested in geology, and published memoirs on the thermal springs of the Pyrenees, on the extinct volcanoes of the Vivarais (Ardeche), on the geology of the Cuchullin and Eildon hills, &c. In addition to about 150 scientific papers, he wrote Travels through the Alps of Savoy and Other Parts of the Pennine Chain, with Observations on the Phenomena of Glaciers (1843); Norway and its Glaciers (1853); Occasional Papers on the Theory of Glaciers (1859); A Tour of Mont Blanc and Monte Rosa (1855).