KiXAHA>r — On Granitic and other Ingenite Rocks. 129 



The granite graduates through 

 gneiss into schist. 



A foliation more or less con- 

 spicuous is often present, or, if 

 it is absent, the large crystals of 

 felspar ai'e often arranged in lines, 

 not perhaps visible in small pieces, 

 but often very conspicuous when 

 the rock is viewed in mass. 



JS^early always porphyi-itic and 

 coarsely crystalline. The felspar 

 that is usually conspicuously de- 

 veloped being the pinkish or flesh- 

 colour, rarely the white. 



Never graduate into elvanyte. 



The granite never 

 into gneiss or schist. 

 IS^o foliation. '"■' 



ffi'aduates 



Often more or less evenly crys- 

 talline, none of the felspars being 

 conspicuously developed. AVhen 

 porphyritic, the white felspar 

 (adularia) often gives the charac- 

 ter, and sometimes the green. 



May graduate into elvanyte, 

 and through elvanyte into f elstone 

 (euiyte), or perhaps even whin- 

 stone. 



iretamorphic-orthoclasic, or higMi/siliceous-granite. — The rocks be- 

 longing to this group may occur as masses, dykes, or beds, according to 

 the position the plutonic rocks, fi-om which they were altered, occupied, 

 "equally they are of a fine even texture, and in some it is probable all 

 the felspar and quartz have not crystallized out from the original 

 felsitic mass, such a rock being the passage-rock into granitoid- 

 felstone. These rocks, when weathered, have not the well-marked, 

 rough, rugged aspect of a typical granite, nor yet the smooth weather- 

 ing of a felstone, but rather a mixtui'e of both, like the weatheiing of 

 a f elspathic sandstone. ^Tien typical, the principal minerals they con- 

 sist of are quai-tz, orthoclase, and mica, pyrite also being usually 

 present ; such rock being metamorphic-petrosilex, or orthoclase-f elstone. 

 From being highly-siliceous they may graduate into a metamoi'phic-oligo- 

 clasic-gTanite, or a homblendic-granite, following the different grada- 

 tions of the plutonic rocks, fi'om which they originated. In rocks of 

 this group it is not unusual to find lines, or a riban, having an 

 aspect somewhat like stratification due to bands of different colour, 

 texture, and perhaps also composition. The bands, or layers, may be 

 coarser or finer than the rest of the rock, or they may be more 

 micaceous, quartzitic, or felsitic, or they may contain minerals, 

 not essentials otherwise, of the rock. They are probably due to a 

 stracture in the original rock, perhaps the Hnes of viscid-fusion, or 



* In this area there seems to he no foliation, or trace of foliation, nevertheless in 

 certain oligoclasic granites, north-east of Castlebar, eoLinty Mayo, and apijarently 

 belonging to this variety (as they occiu" in dykes and large sewers), there is a distinct 

 foliation. As I never carefully examined these Castlebar rocks I cannot give par- 

 ticulars about them. 



