FRAGMENTS OP OTHER ROCKS CONTAINED IN GRANITE. 15 



portion of the rock, and these are associated with granular quartz 

 and fragments of felspar ; besides which there are often traces of an 

 amorphous felsitic ground-mass. Less frequently hornblende and 

 mica decidedly predominate — quartz, a small quantity of felspar, 

 garnets, and a little pyrites being also present. The hornblende 

 and mica in such rocks generally enclose numerous granules of 

 transparent quartz. 



A fine-grained inclusion from this locality of over a foot in length 

 is composed of contorted bauds varying in colour from light grey 

 to dark green. Under the microscope it is seen to consist largely of 

 a mixture of colourless and dark mica and hornblende, with a few 

 small garnets and a mineral which is probably sahlite, the shade 

 of the several laminae varying with the relative proportions of 

 the different minerals present in each. This rock does not contain 

 much free quartz ; but a few small crystals of orthoclase and of a 

 triclinic felspar, as well as a small amount of a felsitic ground-mass, 

 are present. 



The analysis of an average specimen of this inclusion afforded the 

 following results (sp. gr. = 2*93) : — 



Water J ^g^^metric 



^^^^"^ \ combined '70 



SUica 52-43 



Phosphoric anhydride trace 



Alumina 12*76 



Perric oxide 1*34 



Perrons „ 4*54 



Manganous oxide trace 



Lime 14-16 



Magnesia 9*75 



Potassa 1-09 



Soda 2-94 



99-71 



In many granites inclusions occasionally take the form of more or 

 less perfect crystals of felspar ; and such specimens can only be re- 

 garded as being an extreme development of the enclosure of quartz 

 and mica in crystals of that mineral. This inclusion of other 

 minerals in felspar is a phenomenon well known to microscopical 

 petrologists. 



A good example of a pseudomorphic inclusion of this kind was 

 brought by Mr.Merrifield from Glen Nevis, and on thin sections being 

 examined under the microscope the granite and its included pseudo- 

 morph are found to consist of the same minerals in nearly similar 

 proportions, except that dark mica is somewhat more plentiful in 

 the latter than in the former. The minerals present, in both instances, 

 are orthoclase, a triclinic felspar, dark greenish mica, hornblende, 

 sphene, magnetite, and apatite. 



Irish Granites. — The only Irish granites which I have examined 

 are those of the north-eastern portion of the island ; some of these 



