Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/267

 form, which ends in a muddy stream like the rest of its class. This is a model local ice-system.

Ireland. — On the top of one of the Mourne Mountains are marks which I attribute to a small local system of this kind. The marks are fresh, and a small stream of water runs along the striae downhill, towards a hollow above Ross Trevor and Carlingford Lough, in which are piles of drift arranged in the form of a terminal moraine.

Mookish, in the north-east corner of Ireland, is a tall scarped isolated hill of quartz, with a plateau on the top. The shape of the hill is very like that of Eriks Jokull, in Iceland.

On the sides of Arrigle, near Mookish, are cliffs with talus heaps ; the top is a plateau a few yards square. When glaciers were in Gweebarra a dome of ice certainly stood upon Mookish ; and probably the small remnant of a plateau on the top of Arrigle indicates similar work.

5. Iceland. — Lang Jokull, near Erik's Jokull, is a long hog- backed ridge about thirty miles long, and covered with a sheet of ice. On the western side I could see no bare rock. On the eastern side, riding by Spraenge Sander, I saw that ice moves from the ridge down towards the low lands as water flows down the roof of a house.

At one place a great rock stands out like a garret-window in a roof. The ice splits at the back, flows down the sides, and meets again below at the base of a cliff. The direction of movement can be seen at a glance. The riven ice looks as if a flood had suddenly frozen while rushing down the steep side of this long hog- backed ridge.

The sea-face of the Mourne Mountains seemed to indicate a similar movement at some places ; but I was unable to find striated rocks there. Dun na Cuaich, at Inverary, and Sul Bheinn, in Sutherland, are like this " garret- window " in shape ; and the movement may be seen behind any stone in a moving stream of water.

Donegal. — The general shape of the hill country about the north of Ireland is a series of irregular furrows and ridges which trend from N.E. to S.W. or thereby. The ridge, on which Snow Mountain is the highest point, is bounded on the S.E. by Gweebarra Pass, the deep groove which contains two fiords, several lakes, and two rivers which flow out at opposite ends on opposite sides of Ireland. On the north-western side the ridge is bounded by a shorter furrow called Glen Veagh. North of that groove is a broken quartz range with a similar trend, which includes Arrigle and Mookish, standing apart. It may be said that granite disturbed the sandstone and altered it and shaped the country. But what shaped the granite ?

The Snow -Mountain range, like Lang Jokull in Iceland, sent down a flood into Gweebarra Pass, as I have shown. It also sent off a broad flood northwards. Erom the base of Slieve Snaght water now flows out of a corrie through nearly a hundred lakes, over granite, about eight miles to Dungloe, where a small river enters the head of a short fjord. The whole country is sprinkled with angular blocks of granite, as big as hay-cocks, hay-ricks, and small houses.

VOL. XXIX. — PART I. P