Although properly a northeastern ridge of
Birks and having little topographical
prominence, Arnison Crag was classed as a separate fell by
Alfred Wainwright in his
Pictorial Guide to the Lakeland Fells. That convention is followed here. In support of his decision he referred to it as ‘a low hill with a summit worthy of a mountain’. Birks, which is itself a satellite of
St Sunday Crag, resides on a southwest to northeast ridge. Below the summit and about halfway down the main slope, a level spur juts out eastward and then curves around to the north to run parallel with Birks. At the far end of this subsidiary ridge is the rocky summit of Arnison Crag. The slight col where the Arnison Crag ridge connects to the flank of Birks is Trough Head. To the east of Arnison Crag is the lower portion of Deepdale and the settlement of Bridgend. This flank is rough and includes Aiken Crag and the face of Arnison Crag itself, just below the summit. To the west, separating the fell from the main ridge of Birks, is Hag Beck. This flows northward from Trough Head, passing through the woods of Glenamara Park before issuing into Grisedale Beck just above the main road. Glenamara Park was once a deer park and now contains much broadleaved woodland. Its retaining wall is still largely intact. The ridge from Trough Head to Arnison Crag is fairly level and passes over a series of knolls. One of these- about halfway along- is the true summit, being high. Wainwright and later guidebook writers have chosen to ignore this top because it is grassy and too far back to give an adequate view. This is one of the many reasons why
Wainwrights are a subjective hill list, in contrast to the more numerically based
Hewitts or
Marilyns. North of the summit, the ground drops steeply over two tiers of rock outcrop, the lower one being Oxford Crag. Arnison Crag meets the valley floor directly behind Patterdale village. ==Geology==