18 J. A. PHILLIPS ON CONCEETIONAKY PATCHES AND 



111 addition to inclusions obviously derived from adjacent rocks, 

 there are smaller ones of a somewhat similar dark shade, of which 

 the origin is not so immediately apparent. When sections of these 

 are examined under the microscope, they are found to be composed 

 of granular quartz with a subordinate amount of felspar and a 

 considerable proportion of dark mica; with these are associated 

 crystalline patches of green horDblende porphyritically enclosing 

 twinned crystals of felspar, occasional small garnets, and, exception- 

 ally, minute crystals of sphene. 



Besides included fragments of extraneous rocks, the Goragh-Wood 

 granite encloses bodies which are apparently of concretionary origin. 

 These comprehend all the constituent minerals of the surrounding 

 rock, although not quite in the same proportions as in the normal 

 granite, since they are sometimes of lighter colour, from the com- 

 parative absence of black mica, while in other cases they exhibit a 

 dark shade in consequence of the greater abundance of that mineral. 



Eig. 8, PI. I., represents a concretionary enclosure in the Goragh- 

 Wood granite, one half natural size. Thin sections of this speci- 

 men are found to be composed of quartz, orthoclase, triclinic 

 felspar, black mica, sphene, a few needles of apatite, and some 

 imperfect crystals of magnetite or ilmenite. In these spotted con- 

 cretions the sphene is usually enclosed in white patches consisting of 

 a mixture of felspar and quartz ; and sometimes assumes the form of 

 crystalline aggregations porphyritically enclosing either twinned 

 crystals of felspar or irregular grains of magnetite. In coarse-grained 

 granites concretionary inclusions sometimes affect the form, of more 

 or less imperfect crystals of felspar. 



The porphyritic granite near Bessbrook, which has been opened 

 out by extensive quarries, closely resembles that at Goragh Wood, 

 and appears to be nearly free from inclusions of every description. 



At Moor Quarry, IJ mile south of ISTewry, the granite does 

 not materially differ from that at Goragh Wood, except that, besides 

 exhibiting less trace of foliation, it is somewhat lighter in colour and 

 rather coarser in texture ; under the microscope it is seen to have 

 an essentially similar composition. 



Similar inclusions to those found at Goragh Wood are of frequent 

 occurrence in this granite ; but those which appear to be of concre- 

 tionary origin are relatively more numerous than in that locality. 



All who have carefully examined the Mourne granite appear to 

 agree with regard to its eruptive origin. Professor Hull further 

 regards it as having been intruded among the stratified rocks in a 

 state bordering on solidity, and with £i temperature only sufficient 

 to indurate, but not to metamorphose, the Silurian rocks by which it 

 is surrounded *. 



One of the most convenient localities from which unweathered 

 specimens of this granite and its inclusions can be obtained is 

 Ballymagreehan near Castlewellan, whence were procured the blocks 

 which now form the base of the Albert Memorial in Hyde Park. 

 This quarry is no longer worked, but the rock, which is of a brownish- 

 * Building and Ornamentar Stones of Great Britain, p. 44. 



