325 



The granite of Peterhead differs from that of Aberdeen. It is 

 pink in colour and devoid of white mica. It is, therefore, a granitite. 

 The quartz is often idiomorphic with respect to felspar. Patches of 

 finer grain and darker colour occur in the mass. These patches are 

 richer in mica and triclinic felspar than the mass of the rock. 

 Analyses of the normal granite and one of the patches have already 

 been quoted (see ante, page 311). 



The granite of Beinn Nevis has been referred to by Professor 

 JUDD. W It is a granitite, or hornblende-granitite, in which porphyritic 

 crystals of pink orthoclase are often present. The mass is traversed 

 by veins of eurite and felsite. 



A specimen from Fort William is rich in sphene and bears the 

 closest possible resemblance microscopically to a rock from the Dalbeattie 

 quarries already referred to as a sphene-bearing hornblende-granitite. 

 Near Ballachulish rocks occur which are intermediate between diorites 

 and hornblende-granitites. One of these has already been described in 

 speaking of the diorites. The igneous rocks of the Beinn Nevis 

 district are regarded by Professor JUDD as the denuded stumps of 

 upper Palaeozoic volcanoes. 



The author is indebted to Mr. BARROW of the Geological Survey 

 for specimens of the granite and gneissose granite of Beinn Vuroch in 

 Perthshire and for information as to the relations of the different 

 varieties. He is also indebted to the Director General for permission 

 to refer to the specimens. The chief interest of these rocks lies in 

 the fact that they illustrate the gradual passage of granite into 

 gneiss and schist. The normal rock is a coarsely crystalline 

 compound of felspar, quartz and dark mica. The felspar is both 

 striated and unstriated. Much of the striated felspar shows 

 microcline structure. Most of the quartz occurs in large irregular 

 crystalline grains ; the remainder is in the granulitic condition. Some 

 of the felspar contains minute well-formed plates of a white 

 mica. These plates are arranged in two or more parallel series. 

 The felspar substance occasionally insinuates itself between the quartz 

 grains. Apatite and zircon are also present. The massive granite 

 passes at its margins into flaser- and augen-gneiss. 



The flaser-structure in these rocks is denned by streaks of dark mica 

 and tumid lenticles of quartzo-felspathic material. The white lenticles tail 

 off into the finest strings (see Fig. 1, Plate XLIIL). Under the microscope 

 they are generally seen to contain a large, irregular grain of felspar, 

 showing microcline-structure, surrounded by a granulitic aggregate 

 of quartz and felspar. The tails of the lenticles are formed of 

 this aggregate. The individual grains of the aggregate arc mostly 

 uniform in their optic characters, and it is not always possible 

 to de'cide whether a given grain is composed of quartz or felspar. 

 The use of convergent light will often determine the point and 



(1) Q.J.G.S., Vol. XXX. (1874), p. 293, 



