FRAGMENTS OF OTHEB E0CK8 CONTAINED IN GRANITE. 11 



When thin sections are examined under the microscope they are 

 found to be composed, in addition to orthoclase and quartz, of a large 

 proportion of a triclinic felspar, which Profs. Haughtou and Heddle 

 have determined to be oligoclase*; this granite also contains a colour- 

 less and a nearly black mica, a few minute garnets, and occasionally 

 crystals of apatite and sphene t. A portion of the felspar exhibits 

 cross hatching in polarized light, and the quartz is frequently traversed 

 by hair-like crystals, which are probably either schorl or rutile. 



A subangular inclusion obtained from Eubislaw quarry, two miles 

 west of Aberdeen, is about 5 inches in length, and resembles a contorted 

 fragment of mica-schist. Sections of this specimen are seen to be com- 

 posed of quartz and felspar, with dark and colourless micas. A con- 

 siderable proportion of the felspar is triclinic, and the cleavage-planes 

 of the micas are parallel to the foliation of the rock. One or two small 

 garnets were also observed. Other inclusions from this locality, of 

 nearly similar appearance, but of smaller dimensions, were collected, 

 and on examination were found to have the same composition. 



At Sclattie quarry, near Buxbum, I found a large piece of sil- 

 very grey schistose rock, weighing several pounds, enclosed in granite. 

 Its surfaces, which were in no way altered, were most completely 

 united with the granite, which was itself quite unaltered in the 

 immediate proximity of the enclosure ; the line of junction of the 

 two rocks was therefore perfectly well defined. This inclusion, 

 which has the appearance of a mica-schist or a highly micaceous 

 gneiss, was found to be composed of quartz, felspar, and white and 

 dark micas. Many of the crystals of felspar evidently belong to a 

 triclinic species, while others exhibit cross striation when ex- 

 amined in polarized light. A few crystals of apatite were observed 

 in sections prepared from this inclusion. 



Another inclusion found in the granite of Sclattie has nearly the 

 following dimensions — length 9 inches, width 7 inches, and thick- 

 ness 3 inches. This specimen, which is exceedingly hard, is of a 

 darker colour than the enclosing rock, and exhibits angles which 

 are but slightly rounded. It is distinctly stratified by alternate 

 bands of nearly colourless quartz and of some darker material, and 

 the whole of its exterior is so covered by a layer of black mica as to 

 render its separation from the surrounding granite an easy operation. 

 Under the microscope this is seen to consist, to a large extent, of 

 granular quartz, of which the outlines sometimes appear slightly 

 rounded. With this quartz are mixed a few fragmentary crystals 

 of felspar, of which some belong to a triclinic species, whilst 

 others show cross striation when examined in polarized light. This 

 specimen contains a considerable amount of brown or black mica ; 

 but white mica is also present, although in a less proportion. The 

 quartz and mica occur in more or less distinct layers ; and the black 

 and colourless micas are much interfoliated, their laminae being 

 frequently enclosed in quartz. 



* Haughtou, Proc. Eoy. Soc. vol. xviii. p. 313 ; Hedclle, Trans. Roy. Soc. 

 Edinb. vol. xxviii. p. 2G5, note. 



t One very minute crystal only of sphene was observed in the sections 

 examined. 



