'210 Proceedings of the Royal Irkh Acndeiny. 



without any addition from the igneous rock, have cited chemical 

 analyses to prove the possibility of such a change ; but they seem to 

 me to overlook the evidence of the field itself, and also the interming- 

 ling traceable with the microscope on the margin of inclusions and of 

 veins that look sharp enough to the unaided eye. When a passage 

 from an inclusion to the surrounding rock is clearly visible, the inclu- 

 sion is, as previously remarked, liable to be treated as a " basic 

 segregation."^ Eut it is impossible to assert that the contact-sehists in 

 such a case as that of CashelgolanHill are "basic segregations" from 

 the granite. The latter rock has none the less intermingled its magma 

 intimately with their crystallizing materials. In such a case, the 

 microscope merely refines and carries further the conclusions forced 

 upon us in the field. 



On the rising ground in Ballyiriston, south-east of this junction, 

 there are rapid variations in the constitution of the granite. Yery 

 pure types, free from biotite, merge into darkened types with pink 

 felspars and nests of dark green biotite. (PI. in., fig. 1). The mode 

 of aggregation of this biotite at once suggests its foreign origin ; and 

 this is confirmed by the frequency of lumps of schist, streaked out 

 parallel to the east-and-west foliation, even as far south as half a 

 mile from the visible junction on the road. Here, then, on the north 

 side of the dome, the phenomena of Kilgole and Garvegort Glebe are 

 repeated ; the foliated granite is clearly of composite origin. 



If any evidence were required, in addition to that which is so 

 obvious in the field, to show that the inclusions are not the oft-cited 

 "basic segregations," it would be found in the fact that veins run 

 from the sui-rounding granite into these inclusions, and take advantage 

 of pre-existing foliation-surfaces in them. A lump of muscovite- 

 biotite-epidote-rock in the granite south of Bonnyglen Lough is thus 

 penetrated by zigzag veins and tongues of biotite-granite. These 



1 W. Salomon, ojw. cit., Zeitschr. d. deutsch. geol. Gesell., Bd. xlii. (1890), pp. 

 476 and 493, describes certain large masses, resembling concretions, in the tonalite 

 of Monte Aviolo, as shading off into the igneous rock, but being none the less 

 inclusions from the adjacent si-Lists. Great crj-stals of biotite and plagiodase, like 

 those of the tonalite, occur within them ; their outer portions have been melted, 

 and the tonalite-niagma has flowed in along cracks, taking foreign constituents 

 into itself and undergoing thus a chemical modification. Salomon's observations 

 deserve quotation beside those of Lacroix, Sollas, and others, whose conclusions 

 this author to some extent anticipates ; and they have more value from the fact 

 that he elsewhere denies that any extensive modification of the tonalite-magma has 

 occurred through absorption of scliist u])on a large scale (" Uelier Alter etc. der 

 periadriatischen Massen, " Tsch. Mittheil., Bd. xvii., 1898, p. 173). 



