O'Reilly — On the Epidiorite and Mica Schists of Killiney. 23 



much attention at tlie hands of the petrographers. A dyke occurring 

 in the Hebridean gneissic systems of Sutherlandshire, near the village 

 of Scourie, has been examined by the author, and has been already 

 referred to as illustrating the passage of a massive igneous rock into a 

 crystallized schist. It also illustrates the passage of a massive plagio- 

 clase-pyroxene rock into a massive plagioclase-hornblende rock (epi- 

 diorite (see pi. 20). 



"The gradual replacement of the pyroxene by hornblende is the 

 most striking figure. The resulting hornblende may be fibrous actino- 

 lite or compact." 



(The fig. 25, three-fourths natural size, represents well the 

 Killiney rock under consideration.) 



At p. 200 he says : — 



"There seems no reason to doubt that the change of the plagio- 

 clase-pyroxene rock to epidiorite and hornblende schist as the result 

 of the dynamic metamorphism which has affected the district. 

 Where there has been no differential movement in the rock-mass, we 

 have the massive epidiorite ; where differential movement has taken 

 place, the schist has been produced. Why certain portions of the 

 dyke have retained their original characters, whilst other portions 

 have been so completely metamorphosed, we cannot at present explain 

 Many dykes similar to that of Scourie doubtless occur in the Highlands 

 of Scotland ; and it is quite possible that many bands of hornblende 

 schist may represent dykes, or sheets, which have been incorporated, 

 as it were, with the general gneissic series." 



That the mica schist beds of Killiaey have undergone meta- 

 morphism, and that the epidiorite in question is a result of that 

 action there, is suggested, all the more strongly the more carefully 

 the ground, as a whole, is studied. On p. 32 of the Memoir cited 

 occurs a foot-note by Professor Hull, with reference to the excellent 

 sketch, by Du ISToyer, of the south-east end of the line of junction of 

 the mica schist with the granite, which appears as a woodcut on 

 p. 33 of the Memoir, and which is mainly intended to show the 

 remarkable distribution of the mica in the granite at the point of 

 contact. Professor Hull says: — "The boss of granite figured on 

 p. 33 appears to me to be simply a case of foliation, and an evidence 

 that this portion of the granite is of metamorphie origin." 



The character here presented by the rocks may be traced, more or 

 less clearly, along the main line of contact of the mica schists with 

 the granite, so that if a metamorphie action is to be presumed in the 

 one case, it may equally well be admitted for the rest. 



