224 SIR ARCHIBALD GEIKIE ON THE BASIC AND [Ma) 7 1 894, 



indeed, among the igneous rocks of this country are there to he 

 found more striking examples of these flow-structures and spherulitic 

 lines than at this locality in Skye. 



Now, it will hardly be believed, but is nevertheless true, that 

 these obvious veins and dykes, repeating down to the minutest 

 details the structures of the dykes which can be traced from the 

 granophyre for many yards across the gabbros, are the ' inclusions ' 

 described by Prof. Judd. His account of the shape of his 

 ' inclusions ' is somewhat vague. He speaks of " a number of 

 irregular patches of pale granitic rock " forming " depressions in the 

 basic rock which arc usually filled with debris ; some of the patches 

 show a section several square yards in area." He makes no 

 allusion to the constant linear form of his patches and to the 

 parallelism of their flow-structure and rows of spherulites with their 

 bounding walls ; nor does he seem to be aware that instead of show- 

 ing "a section of several square yards" they can be followed as 

 definite bands for considerable distances. Even the smallest of 

 them takes the form of a linear vein, and not of an included block. 



Of true inclusions — that is, of blocks of older granite caught up 

 and altered by the gabbro — there is not, so far as I have been able 

 to discover, one single example to be found on the whole ridge 

 including Druim an Eidhne. There must be dozens of veins and 

 dykes, not merely within the " 20 or 30 yards from the line of 

 junction " where Prof. Judd observed them, and on the little portion 

 of Druim an Eidhne where he has marked them on his map, but 

 for some hundreds of yards across the ridge along its whole extent 

 of a mile or more. In fact, the ridge is penetrated by many protru- 

 sions of the acid rock, and it is the ends and projections of these 

 veins and dykes, visible at the surface, which Prof. Judd has 

 mistaken for inclusions. 



Let me describe two or three illustrative examples which will 

 serve to show the various aspects of these apparently detached 

 portions of the great acid intrusion. At the point where the foot- 

 path to Coruisk begins to ascend the rugged gabbro ridge, it is 

 crossed by a small stream, and at this locality a well-marked vein 

 of felsitic rock runs through the gabbro. If the observer turns 

 northward from this point, up the craggy surface of Druim an 

 Eidhne, he will, at a distance of about a hundred yards, come upon 

 another vein, varying from 1 to 3 feet in breadth, traceable for 

 20 feet, and exhibiting the most perfect flow-structure, parallel 

 to the walls, with rows of large, and sometimes hollow, spherulites. 

 A few yards farther up the hill, another exposure (which may be a 

 further portion of the same dyke) displays the relations represented 

 in fig. 2 (p. 225). The portion of the dyke visible is about 18 feet 

 long and 6 feet broad. The rock is a fine granular felsite or close- 

 grained granophyre, with exquisite flow-structure, which not only 

 keeps parallel to the boundary-walls, but follows all their irregu- 

 larities of contour, its lines curving round projections and sweeping 

 into eddy-like swirls, in such a manner as vividly to portray the motion 

 of a viscous lava flowing in a cleft between two walls of solid rock. 



