12 . J. A. PHILLIPS ON COK-CRETIONARY PATCHES AlfD 



The inclusions found in the grey granite at Dyce quarry, six 

 miles north-west of the city of Aberdeen, are, for the most part, 

 foliated subangular masses of a dark bluish-grey colour, not unlike 

 the first of those described as having been obtained at Sclattie. 

 They are all distinctly foliated, and, on sections being examined, 

 are seen to be composed of quartz, felspar, and the usual dark- and 

 light-coloured micas; these inclusions also contain a few minute 

 garnets, and a little magnetite, together with occasional needle- 

 like crystals of apatite. Some of the bands of this enclosed rock 

 are almost entirely composed of the two descriptions of mica, while 

 others decidedly resemble gneiss in their constitution. 



One of the most remarkable specimens from this quarry was in the 

 form of a lenticular mass weighing considerably over a hundredweight, 

 and so covered externally by a thin layer of mica that it readily sepa- 

 rated from the enclosing rock. On being broken it was found to 

 consist of a granite possessing the same characteristics as that around 

 it, but at least one half finer in texture. Sections were prepared 

 from the fragments, and were found to be composed of the same 

 materials as the enclosing rock, with the addition of a little 

 magnetite, the presence of which was not observed in the latter. 

 Triclinic felspar (oligoclase) was also more than usually abundant. 



At Kemnay, three miles west of the railway- station atKintore, a 

 quarry is extensively worked on a granite of the same general cha- 

 racter as that wrought nearer the city of Aberdeen. In this locality 

 inclusions are extremely rare ; but one of the specimens there ob- 

 tained is of great interest as affording evidence that some of the dark 

 patches in granites, which at first sight closely resemble enclosures 

 of a schistose rock, may in reality be the result of segregation. 



Pig. 6, PI. I., represents the specimen referred to, one half natural 

 size. 



Sections of the dark material forming the inclusion in this rock are, 

 when examined under the microscope, found to be composed entirely 

 of black and colourless micas with their planes of cleavage all lying 

 approximately in the same direction. 



The granite in this quarry is traversed by a dyke of very fine- 

 grained black mica-trap, which has sometimes a thickness of several 

 feet, but sends off various branches, some of which are not much 

 thicker than cardboard. This trap is so firmly soldered to the en- 

 closing granite that blocks of which one portion is granite and the 

 other trap do not, when struck, show a greater tendency to divide 

 along the junction than in any other direction. When cut perpen- 

 dicularly to the plane of junction, the granite and trap are seen to 

 be joined along a line as distinct as when two pieces of differently 

 coloured wood are planed to a joint, glued together, and subse- 

 quently polished. Some small fragments of granite which have be- 

 come enclosed in this trap are not in the slightest degree altered, and 

 their edges are as sharp as when first separated from the parent rock. 



Under the microscope this trap is found to consist of a crystalline 

 felspathic ground-mass in which small flakes of dark mica and di- 

 stinct crystals of felspar are porphyritically enclosed. The crystals 



