The most continuous of the low morainic ridges runs from the meander loop of the Stonethwaite Beck by the roadside south of Rosthwaite in an arc across to the Derwent bank opposite Longthwaite, thence southward to near Borrowdale ChurchWeekend breaks in the Lake District. Opposite Longthwaite the River Derwent has cut into the moraine and exposed its constituent boulders, gravels and clays. Further moraines indicating subsequent halts during the general retreat of the valley glacier southwards into the mountain fastness occur around Great End. Perhaps the most impressive of the morainic ridges lies at the entrance to the Seathwaite valley, with Thornythwaite Farm sitting imposingly on its crest. The raised site of the farm is necessary because the valley floor upstream is liable to flood, and this in spite of control of the course of the beck.
This valley, the Grains Gill branch of Borrowdale, is one of many which originate in the mountain knot dominated by Scafell and Great Gable. On the leeward side of these high peaks snow accumulation must have been considerable at certain times during the Ice Age. Glaciers in valleys like Grains Gill were thus assured of a plentiful supply of new ice to compensate for the loss due to melting at their snouts. Not surprisingly this area witnessed the full effects of the mini¬glaciation of about 8800 B.C. Upstream from Seathwaite to beyond Stockley Bridge there is an extensive area of hummocky drift with fresh looking mounds lining the valley side above the tumbling beck. The footpath from Seathwaite goes right through the Centre of this glacial dumping ground, climb¬ing one knoll after another. Thus although the glacier probably only existed for about 500 years it has left its unmistakable mark on the terrain.
At Stockley Bridge there is another feature which is associated with the glaciation of the area, although in this case of much greater age than the hummocky drift. Mter cross¬ing the bridge the path climbs steadily up to the lip of the side valley drained by Styhead Gill . This hanging valley lies some 500 feet above the main Grains Gill and the stream descends in a series of waterfalls Taylorgill Force. Hanging valleys of this type, a result of the greater deepening of the main valley floor by the glacier compared with that of its tributary ice streams, occur widely in the Lake District. Some, like that of Sourmilk Gill above Seathwaite , are the outer lips of combes lying high up on the valley side. The climb to the Hoister Pass from the floor of Borrowdale is also up a hanging valley. Once on top the valley near the Pass is wide and open and there are the same conical mounds of hummocky drift as are found at Stockley Bridge. The upper part of Borrowdale, with its converging valley systems, has a wealth of glacial topo¬graphy, which the early traveller would never have suspected.
The limit of his penetration was usually the Bowder Stone , a great upended mass of rock weighing perhaps 2,000 tons. Even the journey from Keswick to see this wonder at the entrance to Borrowdale was not to be undertaken lightly, if the eighteenth century guidebook accounts were to be believed. Thomas Gray, who made a tour of the Lakes in 1769, in an exaggerated piece of descriptive writing, com¬pared the journey into lower Borrowdale with that in the Alpine passes, 'where the guides tell you to move with speed, and say nothing, lest the agitation of the , air should loosen the snows above, and bring down a mass that would overwhelm a caravan.' In spite of Gray's warning it is clear that many risked the 'perils' and visited the Bowder Stone, speculating on how it could have arrived in its precarious situation.
On the east, Borrowdale is bordered by the plateau country which rises to about 2,000 ft along its watershed crest. Although parts of the top are extremely flat and boggy, the land soon falls away to the next major valley, that containing Thirlmere. With the raising of the level of this natural lake by Manchester Water Corporation in 1906, the whole valley was transformed in appearance. In place of the valley slopes which tailed off gradually towards the water's edge there was now a steep pitch into the lake.
At its upper end the lake was lengthened and now lay close to the col of Dunmail Raise leading across to Grasmere. This col coincides with a belt of shattered rock, a weakness which ice undoubted¬ly exploited.Masses of hummocky drift were also dumped so that the area by the roadside is not unlike that of the Honister Pass in appearance. At the lower end of Thirlmere, the valley splits into two, one branch forming the Vale of St John's and the other the valley of the Naddle Beck . Ice in the Thirlmere section of the valley probably split into two but it seems that the glacier in St John's Vale was the more powerful of the two. When it finally melted, the river draining the lake chose this route rather than the Naddle valley.