Chaulkswou'ih — Glacial Geology of North- Wast of Irelan d. 231 



as far as Draperstown on the margin of tlie area under review. The granites 

 and other rocks of Slieve Gallion have also been carried in the same direction, 

 and are encountered all along the Baun, as far north as Coleraiue. 



No boulders of these Slieve Gallion rocks were observed south of their 

 outcrop. This furnishes strong confirmatory evidence of the view maintained 

 in an earlier section of this paper, and based chiefly on the sections south- 

 west of Draperstown, that Scottisli ice never had access to this region nor 

 to the " Omagh-Drapei'stown corridor." 



The Tyrone granites and aphanites have been encountered as far east as 

 the western shores of Lough Neagh, and were observed by Dr. A. E. 

 Dwerryhouse even much farther east, at Soldierstown, beyond the S.-E. 

 corner of Lough Neagh. 



The Fintona Plain was glaciated along its length from the south-west, or 

 west-south-west, towards Omagh and MuUaghcarn. The Fintona Hills, 

 forming its southern margin, were completely overridden by ice from the 

 west and the north-west.' . 



The mass of Slieve Beagh, whieli lies directly on tlie line of the " Central 

 Axis " of E. Hull [cmU, p. 176), was glaciated up its very summit by extraneous 

 ice ; it never nourished local glaciers, nor was it at any period a radiation 

 point or "knot" on an axis of dispersion. 



The limits of dispersal of the Tyrone granites- and associated igneous 

 rocks are indicated on the small map (fig. 1), on which are also inserted the 

 position of the outcrops. 



These rocks possess such general affinities, that it was found difficult, 

 indeed frequently impossible, to determine the parent source of any 

 particular boulder. 'J'his uncertainty of determination is rendered all the 

 greater because, as Professor G. A. J. Cole has pointed out in his paper 

 descriptive of the granites and associated rocks,^ " a good many areas of the 

 granite may still be hidden under bogland." The rocks of whole areas are, 

 moreover, " seamed with granite and microgranite." Their general character- 

 istics are, however, so extremely clear, that tliei-e is seldom much difficulty 

 in assigning surface erratics or boulders in the drifts to this group of acid 

 rocks. The distribution of these granite erratics is fully confirmed by that 

 of tbe aphanites or the basic rocks with which they are so intimately 

 associated. 



The granite erratics have been observed over all the country of the 



^ E.g., striae going S.-E., observed uear the summit of Brougher Muuntciin, oneof the 

 highest parts of the whole range. 



- Their petrology has been briefly referred to in au earlier section (p. 182). 



' On Bletamorphic Rooks in Eastern Tyrone and Southern Donegal.— Trans. Roy. 

 Irish Acad., vol. xxxi (1900), p. 431. 



