The headwaters of the Esk and Duddon are separated by a ridge falling south west from the summit of Crinkle Crags. This line of high ground continues over many twists and turns for 15 miles, finally meeting the sea on the slopes of Black Combe. From Crinkle Crags the first fells on this ridge are Hard Knott and Harter Fell, separated by Hardknott Pass. From Harter Fell the ridge continues over Green Crag, Great Worm Crag, Yoadcastle, Whitfell, Buck Barrow and Black Combe. Alfred Wainwright considered the latter hills unworthy of inclusion in his influential Pictorial Guide to the Lakeland Fells, stating that south and west from Green Crag the scenery quickly deteriorates. This summit has therefore been taken as the boundary of fellwalking country. Later guidebook writers have disagreed, adding and the remainder of the range to their main volumes. Wainwright himself later relented and included these lesser hills in a supplementary volume, The Outlying Fells of Lakeland.