Tol. 50.] ACID ROCKS OF THE INNER HEBRIDES. 221 



prominent rib may be observed rising amid the ordinary granophyre. 

 It consists of a spherulitic tine-grained material forming a band 

 about 10 feet broad, which may be traced under the debris for 

 several hundred yards up the hill in a direction slightly north of 

 west. It exhibits the same beautiful flow-structure with spherulites 

 as is seen in the marginal part of the granophyre boss. The 

 spherulites, often an inch or more in diameter, are set in rows 

 along the lines of flow-structure, which run parallel to the direction 

 of the rib. The absolute identity of these structures with those 

 which I have described and with those also of the dykes and veins 

 to be immediately referred to, including those of the so-called ' in- 

 clusions,' is so obvious that there cannot be any room for hesitation 

 in classing them all together as having one common origin. The 

 presence of a band of spherulitic granophyi'e or felsite in the main 

 body of the granophyre, at a distance of 1000 feet from the edge of 

 the gabbro, cannot be accounted for by any fusing effect of the basic 

 rock. Like the marginal zone of finer grain, this internal dyke-like 

 rib obviously represents a phase in the consolidation of the great 

 protrusion of acid material, though its production may have been 

 somewhat later than that of the marginal zone and its offshoots. 



I now proceed to show that the great granitic eruption of Glen 

 Sligachan has been accompanied by the injection of dykes and veins 

 into the adjacent rocks, as formerly affirmed by me. About half a 

 mile south from the top of Meall Dearg, and thus well to the north 

 of the locality at which Prof. Judd has shown the position of his 

 ' inclusions ' on his map, the low gabbro cliff, where it overlooks the 

 sources of the streamlets that run down the declivity below, is 

 interrupted by several hollows which allow of an easy ascent to the 

 summit of the ridge. On examination it is found that these inter- 

 ruptions in the line of cliff are due to breaks in the continuity of the 

 various beds and veins of different gabbros, and to the divergence of 

 dykes of granophyre from the main body of that rock. Three such 

 interruptions may be observed within a horizontal distance of 

 90 yards (fig. 1, p. 222). Each of these marks the position of a dyke 

 which can be followed from the spherulitic margin of the granophyre 

 with which it is continuous and of which it forms an offshoot. 



The most northerly of the three dykes (I.) is about 9 feet wide 

 where it issues from the main mass of granophyre. Weathering 

 more easily than the basic rocks through which it runs, it occupies 

 the bottom of a long hollow of which the various sheets of gabbro 

 form the craggy sides. But it protrudes at numerous points from 

 under the turf, and by means of these projections can be followed 

 in a nearly straight line in a S.S.E. direction for 800 feet, when it 

 is lost beneath herbage and masses of gabbro. 



The second dyke (II.), from 6 to 8 feet broad as it leaves the 

 granophyre mass, runs parallel to the first at a distance of about 30 

 yards from it, and can be traced for 200 feet or more southward 

 across the gabbro. There is in this case also no difficulty in 

 following along the line of straight hollow the protruding knobs, 



