Southern Howgill Fells
These unusually shaped hills are formed from an outcrop of sequences of sandstones, siltstones and mudstones of Silurian age which contrast markedly with the igneous formations of the Cumbria High Fells to the west and the limestones of the Yorkshire Dales to the east and south east. Although the geological structure is relatively complex, the rocks all possess a similar resistance to erosion, which gives rise to the smooth, rounded shape that is so characteristic of these fells. Ice scouring during the last glaciation has only acted to emphasise the evenness of the slopes.
The rocks that make up the Howgill Fells are of pre-carboniferous origin. In the Cautley Spout area, close to the Dent Fault, there are outcrops of dark shales of the Upper Ordovician age. The bulk of the Howgills, as well as Middleton and Barbon Fell to the south, are the Silurian age (430-415 million years old), and some 60 million years older than the Carboniferous rocks that make up most of the Yorkshire Dales National Park. The Howgills are almost entirely composed of a very hard and compact sandstone – the Coniston Grit. Being uniform and resistant to weathering, it has produced rounded summits rather than rocky crags.
The most important feature of the geology of the area is the Dent Fault. The fault is the result of intense pressure caused when the rocks of the Lake District rose up some 2,400 metres against the horizontal strata on the Pennine side, pushing the limestones into a vertical position close to the fault plane. The fault, which is 32km in length between Kirkby Stephen and Kirkby Lonsdale, is a classic example of a reverse fault and forms the physical division between the two contrasting types of scenery – the smooth flanked Howgills and the horizontal limestone scars of the Yorkshire Dales.
Although the mountain mass of the Howgills was large enough to have its own ice cap during the last Ice Age, ice from the Lake District and Pennines may have hemmed the Howgills in ice, reducing the amount of erosion that could take place. The rounded summits therefore show very little glacial erosion. Cautley Crags are the only glacial features, where the cliffs rise up from behind the beginnings of a corrie, the higher valleys of Red Gill and Swere Gill being hanging valleys.
Several small streams flow off the hilltops and down the gills in a radial pattern from the central core, to join the River Lune in the north and west, and the Rawthey in the east and south.
