220 ■ Proceedings of the Royal Irish Academy. 



of the area of dispersal,- and to define the track along which tlie boulders are 

 more especially minierous. Their dispersal is indicated on the map (fig. 1) 

 and on tlie general map (PI. IX). 



Within this tract it was fonnd impossible to single out any special 

 trains of grfpiiilic dSbris, as the granite is too homogeneous over its outcrop. 

 Moreover, tlie finer-grained veins and off-shoots of granile and pegmatite 

 are, as in the case of tlie Donegal granite, where they are more generally 

 developed, too irregularly distributed to indicate special lines of flow, thougli 

 boulders from these sources can be detected in the drifts. 



All that can in consequence be definitely affirmed is that in the centre of 

 tlie tract the boulders are generally lai-ger and more numerous, becoming less 

 so as we proceed to the margin, where they finally occur singly and at 

 considerable intervals. Their sporadic occurrence towards the border and 

 the fewness of good drift sections along this line have made it impossible 

 to assign more than approximate boundaries to this boulder country. The 

 exactness, moreover, with which the line can be drawn varies over different 

 parts of its length according to the opportunities that natural and artificial 

 sections offer for the examination of tlie drift. On the surface of the boulder 

 fan and in exposures outside its margin, no boulder or pebble of the granite 

 was detected, with the few exceptions to be mentioned presently. 



As the Barnesmore granite mass lies astride the main ice-shed of Donegal, 

 its erratics have travelled northward and southward from the axis, the train 

 of boulders on the north extending from the granite outcrop to the seaward 

 end of Lough Swilly and of Lough Foyle, on the south, as far as St. John's 

 Point in Donegal Bay. No granite erratics from Barnesmore were detected 

 on the surface of the bare limestone country east of Ballyshannon. To the west 

 of a line through Barnesmore, Straness, Brown Hall (E. of Ballintra), and 

 Ballyshannon, the granites are fairly plentiful, both in sections and on the 

 surface, and become increasingly numerous as we proceed to the eastern shores 

 of Donegal Bay and the line of the railway from Donegal Town to Barnesmore 

 Gap. 



Countless granites lie strewn along the beach from Donegal Town 

 westwards, doubtless derived from the truncated drumlins. Boulders also 

 occur very abundantly over all the peninsular tract, running to the east of 

 Inver Bay and over the surface of the small peninsula ending in Ball's Hill, 

 likewise over the country to the north of Inver and in the railway cuttings 

 between this place and Donegal Town, They were observed in good numbers 

 in the cliff sections round the St. John's Peninsula. They were noted as far 

 as Heelin Port. 



Proceeding westwards, these boulders cease to be plentiful beyond Kiln 



