420 31K. G. BABROW ON THE MOINE GNEISSES [Xov. I904, 



essentially that of a very fine or less crystalline Moine Gneiss, 

 but there is little microcline present, and the biotite is reddish- 

 brown. Another specimen of the more muddy, but still parallel- 

 banded material, was taken from the Tilt close to Marble Lodge 

 (10,556). This is grey throughout, but the darker bands were 

 clearly finer mud originaliy. These are rich in red biotite and 

 white mica associated with plagioclase, in exactly the same way as 

 in parts of the Dark Schist to be described later. The lighter bands 

 are composed of quartz and decomposed plagioclase, with a little 

 microcline, and possibly some orthoclase. A little biotite, chlorite, 

 and white mica are also present. This rock thus forms a link 

 between the more quartzose, banded material and the curious 

 felspathic and micaceous rock, containing much dark dust, which is 

 so typical of the Black Schist near the Little Limestone. 



Returning to the little stream, above Gilbert's Bridge, at the 

 northern end of Dalginross Wood, and examining its bed, we find 

 the change in the nature of the parallel-banded rocks taking place 

 far more rapidly, for we now cross this zone at right angles, instead 

 of diagonally. 



The section below Gilbert's Bridge shows phenomena essentially 

 similar to those already recorded. It is, however, far more difficult 

 of access, and the absence of bends, and the fact that the river runs 

 more nearly along the course of the strike, make the progressive 

 change less clear. There are, nevertheless, a few points of special 

 interest. The band nearest the limestone in the Moine Gneisses 

 is often a pure white quartzite, which can be distinguished from 

 the white margin of the Main Quartzite only by the fact that it 

 does not weather rusty-brown. As before, small patches of Dark 

 Schist occur occasionally between the Limestone and the Gneiss, and 

 one of these, 250 yards below the bridge, contains a considerable 

 quantity of kyanite. 



At the sharp bend of the Tilt in Crombie Wood (see map, 

 PI. XXXIII) there is an especially-fine exposure of the Pink Rock, 

 partly in thin pure bands, partly commingled with other material. 

 A little south of Crombie Burn, on the west side of the Tilt, is a 

 small scar, composed of very finely-banded and much less crj'stalline 

 material, showing that a change takes place below Gilbert's Bridge 

 similar to that already described above it. The stages of the change 

 are not, however, so well seen, and the decrease in crystallization is 

 not so rapid. 



(c) The Banvie-Burn Section. 



A section somewhat similar to that of Gilbert's Bridge occurs in 

 Ban vie Burn, at the Whim Plantation, to the north-north-west of 

 Blair Castle. At the western edge of the wood, close to the burn, 

 the typical Moine Gneisses are exposed in a quarry (already referred 

 to, p. 409), and, descending the stream from this point, we cross the 

 usual parallel-banded rocks, locally more siliceous, until we reach 



