ORIGIN OF ANGLESEA AND LUNDY ISLAND. 129 



the opposite coast of County Down. Geographically the Isle of Man 

 belongs to Cumberland and Lancashire, because an elevation of not 

 more than a hundred feet would again join it to those counties. The 

 shallow sea which severs it from the North of England has probably 

 been ploughed out in part in comparatively recent times. 



Anglesea. The Isle of Anglesea is divided from Wales by a 

 channel scarcely wider than a river ; and it is not easy ac- 

 curately to determine how the separation was effected ; but 

 Professor Eamsay has remarked that with the exception of Holy- 

 head and Garn, the general level both of the island and of the 

 opposite parts of Caernarvonshire is low, not rising more than 

 two hundred feet above the sea. He observes that the rocks are 

 smoothed with ice-marks, and scored with glacial striae, which run 

 towards the south-west ; and that the country is covered with 

 boulder clay full of angular fragments, such as a glacier would 

 carry or deposit. These glaciers could not have originated in the 

 mountains around Snowdon ; and it is concluded from the rock 

 fragments deposited that the glacier must have come from high land 

 farther north in fact, from Cumberland and the mountains about 

 Criifell in the south of Scotland, probably at a period when the 

 level of Britain was higher. A glacier of this large size would 

 have passed between the coast of Cumberland and the Isle of Man. 

 It not improbably scooped out the shallow sea between them. It 

 received a tributary glacier coming down from Morecambe Bay ; and 

 passing over the whole of the Isle of Anglesea may have excavated 

 the Menai Straits, as Professor Ramsay suggests. But since car- 

 boniferous limestone forms much of the shores -of the Menai Straits, 

 it is impossible not to suspect that, though filled with ice in a glacial 

 period, this channel may have originated in times far more remote 

 as a sort of canon. Thus, both the Isle of Man and the Isle of 

 Anglesea belong to a class of islands, of which the existence is 

 directly attributable to denudation. 



Lundy Isle. A third group of islands may be typified by Lundy 

 Island in the Bristol Channel and the group called the Channel 

 Islands. These appear to owe their existence rather to the durability 

 of the rock of which they consist that is, to their greater power of 

 resisting denudation than to other causes. They are granite bosses 

 similar to those which would remain at the Land's End, about 

 Falmouth, St. Austel, Bodmin Moor, and Dartmoor, if the level of 

 Cornwall and South Devon were to be lowered. They are with- 

 out doubt indications of axes of upheaval. It is even possible, as 

 suggested by Professor Judd in the case of Lundy Isle, that they 

 may have been the central cores of old volcanoes ; but it is also 

 quite possible for granite to be formed by pressure in the axis of 

 an anticlinal fold, and to cool there without ever bursting through 

 the great thickness of over-lying rock which originally covered it. 

 The attempts made by Mr. Sorby to estimate the pressure under 

 which granite consolidated, would lead to the conclusion that de- 

 nudation to an enormous extent, involving the removal of rocks 



VOL. i. I 



