192 Proceedings of the Royal Irish Academy. 



The evidence of the Scottish glaeiation of the southern area, south of the 

 Sperrin Mountains, is not exclusively based on the flints and other rocks of 

 County Antrim origin, for the biotite granites of County Tyrone are also 

 involved. Space forbids a detailed description of their distribution. A few 

 localities on the outer margin of their occurrence may, however-, be mentioned ; 

 the others may be comprehensively dismissed by the statement that within 

 the boundary so delineated flints and other eastern erratics occur sporadi- 

 cally in the drift sections. 



To the west of Donaghmore, along the foot of the O.E.S. hills, flints begin to 

 appear. They are present in sections at Greyslones witli local Carboniferous 

 rocks. The flints are baked and unbaked, and are accompanied by a few 

 granite boulders. At Upper Kerrib (and in other sections in gravels in its 

 vicinity and to the south of the railway) flints occur in extraordinary abun- 

 dance, both baked and unbaked varieties, with a few pieces of chalk and 

 boulders of granite. In the Donaghmore area flints are plentiful. Tliey were 

 also found in gravel sections near Cavanacaw hough, with some pyroxenic 

 rocks and granite from Tyrone. A similar assemblage was observed in the drift 

 near Moree House, some 3i miles east of Pomeroy. At Smotan Jdridge on the 

 eastern slopes of Slieve Beagli, at an altitude of ca. 500 feet O.D., very good 

 exposures show drift containing — besides pebbles and boulders of local Car- 

 boniferous limestone and grits and a few porphyries from the O.E.S. tract to 

 the north — one granite boulder aud a few flints.' The paisanite of Ailsa 

 Craig has been found at Monaghan and near Cookstown. 



The abundance of the flints in this area is doubtless due to the largeness 

 of the outcrop of chalk to the south-east of Lough Neagh. This outcrop, as 

 other evidence shows, lay directly in the path of the Scottish ice which 

 overrode the country around Donaghmore. The possibility of unknown 

 outliers of chalk concealed beneath these thick drifts may not, however, be 

 ignored. 



The western limit of the eastern erratics may now be briefly sketched, 

 proceeding from north to south. Coincident with the line of Lough Swilly 

 to the west of Inishowen, it runs roughly along the Pennyburn depression, 

 which separates the hills of Inishowen from those to the south — flints are 

 absent from the drifts S.W. of this valley. Lrcluding the city of London- 

 derry in the area covered by the eastern drifts, it swings across the foot hills 

 of the Sperrin Mountains to the hill of Loughermore,^ along the east side of 



* Chalk and chalk-flints have been observed in the country to Lho south of this, 

 among other places at Annyart, near Castleblayney. (Mem. Geol. Surv., Sheet 59, 

 p. 24.) 



" The erratics of green schist, coarse epidiorite, and laraprophyre noted by Professor 

 Seymour (Londonderry Memoir, p. 73) in the district south of this line are far more 



