The Lhvyd^nor Bach Granoiihyre. 359 



trace of granophyric iutergrowtli is lost, and the rock becomes 

 normall}' granitoid. 



TI. The Granophyre. 



Fairly fresh specimens are easily obtained. Hand specimens 

 from the centre of the laccolith present a patchy appearance, with 

 dark aggregates in a pink matrix. The dark coloured basic patches, 

 which are almost invariably rounded, appear to constitute about a 

 quarter of the rock, and vary considerably in size ; ovoid masses, 

 more than 2 inches across, have been observed. In the leucocratic 

 portion, idiomorphic felspars, surrounded by pink micropegmatite, 

 are abundant. 



Under the microscope the rock is seen to consist essentially of 

 various felspars, quartz, pyroxene, secondary amphibole, and 

 chlorite. The dominant felspar is an idiomorphic plagioclase, 

 often badly weathered, but containing many fairly fresh portions, 

 which, by their well-developed albite twmning, enable the felspars 

 to be determined as oligoclase. The refractive indices of these 

 felspars show that in many cases albite-oligoclase is present in the 

 outer parts of the crystals. Laths of secondary mica occupy a 

 large portion of the weathered phenocrysts : ^these sericite laths are 

 arranged in lines parallel to the felspar cleavage. 



The boundaries of these idiomorphic felspars are well marked, 

 often by a " dirt " band, and practically all are surrounded by a 

 growth of a microperthitic felspar, which is presumably near to 

 anorthoclase in composition. 



The anorthoclase zone is itself surrounded by micropegmatite. 

 The graphic intergrowth shows the usual variations in arrangement, 

 due to differences in grain. It is frequently in optical continuity 

 with the outer, or anorthoclase, zone of the larger felspars. 



Quartz is fairly abundaiit, occurrmg both interstitially and in 

 granophyric intergrowth with the felspars. It is frequently present 

 in the form of a mosaic, along with microperthite and an un twinned 

 water-clear felspar, which has a refractive index less than quartz. 

 The mosaic appears to have some relation to the clots of basic 

 material, since it generally occurs, j^artially but not completely, 

 surrounding the patches of ferro-magnesian minerals. This type of 

 quartz contains characteristic lines of gas and solid inclusions, 

 includmg needles of amphibole and small albite crystals, and 

 apparently is not of secondary origui. Most of the inclusions are 

 confined to the inner areas of each mosaic. The micropegmatitic 

 quartz exhibits every gradation from that of a relatively large 

 crystal of quartz containing thin bands of felspar, to the finest 

 intergrowth. Micropegmatite is not limited to areas surrounding 

 the felspar phenocrysts, but occurs also as a interstitial constituent, 

 in the body of the rock. 



The majority of the ferro-magnesian minerals are segregated 

 throughout the rock in groups, which in certain respects may be 



