III.—On the Surface–Geology of the Lake–District

Extract

The following notes were made during a few days' leave of absence, spent chiefly on the Green-slate area of the Lake-district, the beds of which have an east-north-east and west-south-west direction of strike, extending across the country in a belt about fourteen, miles in width, resting on the Skiddaw Slates, and passing under the various divisions of the Coniston series. The characteristic feature of this tract of country is the uniformity in direction of all the gorges, or depressions, in which the lakes occur. The initiative of their direction (as pointed out by Dr. Nicholson) appears to have been given by a system of north and south faults: thus Windermere, Rydal Water, Grasmere, and Thirlmere may be said to lie in one line of depression. Between the two last-mentioned lakes the pass of Dunmail Raise forms a col between two valleys. In the bottom of the valley, between the pass and Grasmere, there are immense mounds of moraine, matter, the pebbles are all angular and strictly local. Steel Fell and Seat Sandal form two cliffs on either side, that on the western being much the steeper; the summit of Helm Crag, being much weathered, forming the well-known “couchant lion with a lamb under its nose,” of the guide books. Following up the ice marks of Easdale Valley into that of Raise Beck, there seems little doubt that the two glaciers occupying these valleys united between Silver How and Nab Scar, and thence bore down upon Loughrigg Fell, which stopped its forward progress in a direct line, deflecting it into what is now Rydal Water. The lake Grasmere is excavated in a rock-basin, and one can easily understand its excavation being due to the immense pressure of the ice infringing on Loughrigg Fell. A similar state of things took place at the foot of Rydal Water; the rocks here are moutonnèed and glaciated upwards.