332 [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. 324 ) 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. Eoy. 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). 



