322 ME. ALFEED HAEKEE ON THE [May 1 896, 



Compared with, what may be called the normal granophyres of 

 the district, these rocks are darker and manifestly richer in the 

 iron-bearing minerals. Examination shows, too, that they are 

 decidedly denser : ten specimens gave specific gravities ranging 

 from 2*56 to 2-73, with a mean of 2- 66, while twenty specimens of 

 the normal granophyres of the district gave from 2*51 to 2*66, with 

 a mean of 2-58. Closer inspection often reveals a mottled appear- 

 ance, due to the dark minerals tending to cluster in vaguely defined 

 patches, and in places these patches become more distinct and are 

 seen to represent enclosed fragments of some basic rock. In other 

 respects, for example, in the prevalence of the micrographic structure, 

 in the drusy character of the more coarsely textured type, etc., these 

 rocks show a close correspondence with the normal granophyres of 

 the district. It cannot, of course, be asserted that they agreed 

 precisely with the latter as regards the composition of the original 

 magma, but it will be shown that the differences which now exist 

 are certainly due, at least in the main, to the taking up and partial 

 dissolution by the acid magma of foreign rock-fragments of more 

 basic composition. 



It is to be observed that these peculiar granophyres do not occur 

 as marginal modifications of, or as having any visible relation to, 

 granophyres of the normal kind, but as independent intrusions. 

 Moreover, the special characters of these rocks are distributed with 

 considerable uniformity throughout each intrusion. Another point 

 to be noticed is that the enclosed rock-fragments have not been 

 derived from the rocks which border the intrusions as seen in out- 

 crop. Excepting that the most easterly and the most westerly of 

 the intrusions are in part bounded by limestone, the rock in contact 

 is everywhere the volcanic agglomerate. The rock-fragments in 

 the agglomerate are chiefly of sandstone and grit, probably Jurassic, 

 and basalt similar to that of the bedded lavas of the district. The 

 included fragments in the granophyre are in general of gabbro y 

 which I have not detected in the agglomerate. They were there- 

 fore derived from some subterranean source, and, as we have seen, 

 from such a depth as to allow of their becoming distributed with 

 some regularity through the involving magma prior to the con- 

 solidation of the latter in its present surroundings. 



The literature of foreign fragments enclosed in igneous rocks is 

 voluminous, but it gives little information bearing on such a case 

 as the present, where portions of a basic rock have been enveloped 

 and attacked by an acid magma. Indeed, Zirkel 1 remarks that 

 ' caustic ' actio u is not known in the case of fragments enclosed in 

 granites and syenites. The fullest account of such phenomena is 

 that given by Prof. Sollas 2 in his description of the relations of 

 the granite and gabbro of Barnavave in the district of Carlingford. 

 This occurrence has obvious points in common with the one under 

 discussion : some of the differences between the two will be brought 

 out in the following pages. The modifications exhibited by the 



1 ' Lehrbuch der Petrographie,' 2nd ed. vol. i. (1893) p. 593. 



2 Trans. Roy. Irish Acad. vol. xxx. pt. xii. (1894) pp. 477-512. 



