NEAK KEW GALLOWAY. 573 



figure, round the large brown mica on the right, are often of very 

 irregular outline. Here and there is a thick network of black 

 colouring matter ; other parts are free from it. In parts the quartz 

 is quite free from inclusions, but usually contains many highly 

 refracting grains, too small for their nature to be determined with 

 any certainty. 



In working over this microscopical slide, which is rather less than 

 1 inch in diameter, one notices that in about half a dozen places the 

 rock becomes coarser. Two such coarse parts are shown in the 

 figure : round the largest mica-flake, and on the margin of the slide 

 diagonally opposite it. They have a very granitic look ; but the 

 brown mica is the same as that in the rest of the rock, and different 

 from that in the granite, and black colouring matter occurs in 

 them as well as in the finer parts ; so I do not see any reason to 

 suppose them to be injections of granite, although felspar is more 

 plentiful than elsewhere. 



§ 4. Plags and Grits traced along the Strike to the Junction. 



Less than halfway up the hill a rocky ridge is seen ; this, con- 

 tinued by a series of bosses to the margin of the granite, runs 

 parallel to the line of shale exposures just described. The ridge 

 consists mainly of schistose rocks, exactly like those described as 

 altered flags in the stream. In places this rock is interbedded with 

 more shaly-looking bands, with chiastolite, and in others with more 

 quartzose gritty-looking rocks. There are also unaltered shales 

 amongst these rocks. The bosses, which continue the line up to 

 the granite, lie a little nearer the shales, and are of a more com- 

 pact quartzose variety. I suppose them to be the same as the 

 grits which lie in the stream between the schistose rocks and the 

 shales. 



The main differences between different layers of these altered 

 grits and flags, from a part of the hill lower than the first cairn, 

 consist in the character of the garnets and in the nature, size, 

 and quantity of the mica-flakes. The garnets are sometimes well-, 

 sometimes ill-formed ; sometimes they contain inclusions in 

 the centre, sometimes in a ring round the centre, rarely none. 

 The mica is usually the purple-brown variety, but is some- 

 times greenish. Larger flakes of white mica occur occasionally. 

 In the more compact rocks the mica is scattered through the rock ; 

 in the more schistose varieties there are bands of minute flakes, as 

 in the rock described from the stream. The base is essentially a 

 fine-grained quartzite. 



Fig. 7, PL XXIII. gives an idea of the principal varieties. Near 

 the top is a lenticle of clear, large-grained vein-quartz and garnet ; 

 below this is a band with well-formed garnets and small flakes of a 

 greenish mica ; then follows one of the bands of minute flakes, and 

 at the bottom is a variety with larger brown mica-flakes in more 

 continuous lines than those above. 



Both macroscopically and microscopically the rocks show great 



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