A Traveller alighting at Trontbeck station (T of Figure), at the summit level of the Keswick and Penrith Railway, finds himself standing at the north-east corner of a moorland plateau (Matterdale Common), having a mean height of over 1000 feet, and sloping gradually down to the River Glenderamackin (G), which bounds it on the north. The moorland is thickly covered with drift, and rock exposures are scarce, except here and there in the tributaries of the Glenderamackin, which run in a northerly direction from the Helvellyn Range, the principal being Troutbeck (T B) and Mosedale Beck (M B); (the latter is one of many of the same name in the district). That the stones in the drift were mainly brought from the Helvellyn Range is easily seen after a very slight examination; the boulders consist mainly of the more altered ashes and lavas derived from the Borrowdale series of the Helvellyn Range, with occasional boulders of the type of quartz-felsite dyke which penetrate the rocks of Helvellyn and its minor ridges (the best known being the familiar “Armboth and Helvellyn Dyke”); whilst the “Eycott” type of volcanic rock, occurring north of the main outcrop of Skiddaw Slates and having its nearest exposure within a mile of Troutbeck station, is entirely unrepresented. At the north-east corner of the moorland, close to Troutbeck station, a few boulders of mountain limestone indicate the point where the erratics from Helvellyn are beginning to be replaced by others brought from the eastward. The drifts of this moorland and of the region to the north have caused the interesting changes in the drainage of the area which it is the main object of this paper to describe.
The use of mineral interfaces in sand-sized volcanic rock fragments to infer mechanical durability
