882 
[B.N.F.C. 
-erratics across the land ; but some field work is still needed to 
connect distant records with our own neighbourhood. 
Let us compare the north-westerly occurrence of Temple- 
patrick rhyolite (see ante , p .824 ) and frequent chalk and flint 
from Malin to Inishowen Head, recorded by Mr. Close and Mr. 
Harte, 12 in conjunction with evidences of an ice-movement 
northwards of Inishowen Peninsula. Professor Carvill Lewis, 
when visiting Ireland in 1885 to compare British with American 
glaciation, wrote 13 :— “My ideas concerning glaciation have now 
been completely revolutionised. I came to Ireland, expecting 
to find it glaciated from the north. I find instead a complicated 
system of ice streams. A Scotch sheet invaded the eastern 
corner of Ireland, going down to Belfast. The ice-sheet of the 
interior radiated off in all directions.” Again, when driving 
from Buncrana towards Malin, he describes “evidences of a 
great stream of ice moving north and east out of this valley. 
Slieve Snaght and the adjoining hills, together with this water- 
shed, formed a great snowfield. Did the whole ice-sheet of 
Ireland move out on this watershed, or did it only drain a local 
snowfield? The watershed is 500 feet high.” Mr. Close’s 
N.N.W. ice-stream was moving to meet this one at Malin on the 
other side of the same watershed. Coupling these facts with 
the rarity of Ailsa rock west of the Bann and the proximity of 
the great Sperrin range of mountains, where Mr. Kilroe has 
recorded evidence of a glacial movement south-eastward, 14 seems 
to suggest a Sperrin ice-stream meeting the Scottish ice and a 
lobe diverging N.-west, bearing rhyolites and Ailsa with it. To 
ascertain the truth of this purely speculative hypothesis by in- 
vestigating deposits between Killagan and Malin Head should 
be a fascinating bit of work. Although the main mass of the 
intruding ice moved southward, pressing on the Mourne moun- 
tains as it received fresh streams from the heights to the west of 
12. On the Post-Tertiary Geology of Co. Donegal. By William Harte. 
Journ. Roy. Geol. Soc. Ireland.. II., 30-67 (read 1867), 1871. 
13. Glacial Geology of Great Britain and Ireland. By the late Henry 
Carvill Lewis, M.A., F.G.S. Longmans, Green & Co. (1894), p. 118. 
14. Directions of Iceflow in the North of Ireland. T.I.G.S., XLIV., 827- 
833 (1888). 
