﻿Vol. 66. ,] AROUND THE EOSS OF MULL GRANITE. 395 



Koyal Scottish Museum. Many of the localities are at a distance 

 from Newer Granite intrusions. 



In at least two instances tourmaline has been found in pelitic 

 gneiss accompanied by kyanite, as in Mull, namely : — 



(1) Glen Clova (Forfarshire). 1 



(2) Wood Wick, Unst (Shetland). 2 In this latter instance staurolite also is 



present. The specimens are dark garnetiferous biotite-gneiss containing 

 abundantly kyanite and tourmaline. 



Besides the foregoing occurrences tourmaline is, on the other 

 hand, also well known in veins and pegmatites connected with 

 plutonic intrusions, especially in the counties of Aberdeen and 

 Banff 3 ; but the facts here adduced plainly show that tourmaline 

 is common in the Highlands, quite independent of the Newer 

 Granites or other igneous masses. 



The presence of the tourmaline is no indication that the old 

 pegmatites are intrusions of extraneous material. After exami- 

 nation of the heavy mineral grains in a number of sedimentary 

 rocks from various formations, it may be stated that tourmaline is 

 almost invariably present in sediments. If the pegmatites be due 

 to segregation during the regional metamorphism, they represent 

 the most volatile fluid that the sediments could yield. Hence, in 

 composition, they are likely to resemble the apophyses of granite, 

 and they may well contain the tourmaline. 4 



Kyanite has not been recorded in Moine Gneisses elsewhere in 

 the North and North-West Highlands, but it is well-known in other 

 similar rocks, notably in the Lewisian Gneiss near Loch Maree ; in 

 Glen Urquhart (Inverness) in pelitic beds supposed to belong to the 

 Lewisian Gneiss ; and in the Lewisian Gneiss at Glenelg. In the 

 ' East Central Highlands ' it is plentiful in pelitic gneisses described 

 by Mr. Barrow, and by him regarded as belonging to the Moine 

 rocks, notably in the Glen Tilt 5 neighbourhood — in dark schists 

 associated with the ' Main ' or ' Blair Atholl ' Limestone ° — and in 

 •the ' Duchray Hill gneiss. 7 The kyanite in these extensive masses 



1 ' Mineralogy of Scotland ' vol. ii (1901) p. 62. 



2 See specimens in the Heddle Collection, Royal Scottish Museum. 



3 See Heddle Collection, and also Heddle's ' Mineralogy of Scotland ' ; 

 compare too the later Palaeozoic granites of Galloway, Cornwall, and Countv 

 Dublin. 



4 Since writing the above, I have received the following interesting note from 

 Mr. Barrow : — ' By far the greatest amount of schorl, if not the whole of it, as 

 seen in altered sediments is due to aggregation of original clastic schorl. 

 Minute needles of clastic schorl are often extremely abundant in the little- 

 altered dark slates, along the Southern Highland border, especially in certain 

 bands. Where these rocks occur in areas of higher crystalline metamorphism 

 the schorl is aggregated, and now often forms patches or much larger needles 

 easily seen by the unaided eye. In a fair number of cases this schorl is 

 associated with quartz, forming small quartz-schorl segregations.' 



5 Quart. Journ, Geol. Soc. vol. xlix (1893) pp. 346-348 & map (pi. xv), 

 ^ilso figs. 3 & 4 (pi. xvi). 



e Ibid. vol. lx (1904) pp. 419, 420. 



7 Mem. Geol. Surv. (Expl. of Sheet 65) p. 101. 



2e2 



