﻿382 ME. T. 0. B0SW0RTH ON METAMORPHISM [Aug. I9IO, 



These granite patches overlying granulite, however, are very likely 

 only offshoots from the main mass, and the line of junction with the 

 schists is more readily interpreted as the lateral margin of a deep- 

 rooted mass with countless tongues and protrusions issuing from it. 

 It is here considered that the granite exposed in the Ross of Mull 

 is the top of a great abyssal mass, over which the Moine rocks 

 extended as a roof whose former height above the granite forming 

 the present surface increased towards the north-west, and that the 

 inclusions in the granite are fragments of this roof which have sunk 

 in from above. 



At the margin of the igneous mass injection of granite material 

 among the schists has taken place in several ways : — 



(1) Irregular veins and strings, possibly often along fissures 

 and cracks. 



(2) Injections along bedding. — These are very regular and 

 uniform in thickness. The larger bands may be several feet thick, 

 and the direction in which the granite flowed is shown by the 

 bending of the mica-felts at the margins. 



Much thinner bands are more common, and are sometimes so 

 close together that a hand-specimen may show several ; while often 

 they are of such microscopic thinness, that they can only be recog- 

 nized as granite from their field-relations. 



How uniformly these bands may follow the bedding is seen in 

 fig. 2 (p. 380). Here ] the rocks have been steeply folded. Granite 

 now occupies part of the core of the fold occurring to the left of the 

 part photographed. Numerous bands of granite, many of them too 

 thin to be visible in the picture, may be followed right round the 

 fold. A slight thickening of each band at the apex suggests that 

 the rock was sufficiently pliant for the intrusive matter to experience 

 relief of pressure there. 



(3) Injections along strain-slips. — The foliation-planes of 

 the mica-schist (or muscovite-biotite gneiss) are often so rumpled 

 that a set of parallel strain-slip planes has been produced crossing 

 them. The structure is frequently on a large scale, with the planes 

 an inch or more apart. On the coast the waves have sometimes 

 broken the rocks repeatedly along them, producing parallel flat 

 ledges on the cliffs. The granite also has taken advantage of these 

 planes of weakness, and often the granite veins along the bedding 

 are connected one with the other by a set of uniform injections along 

 the strain-slips. This occurs to some extent in the rock figured 

 above (fig. 2, p. 380), but a much better example may be seen almost 

 exactly a third of a mile a little north of west of Loch-an-t-Suidhe„ 

 Here a large part of a hillside facing north is formed of a schist 

 mass included in the granite. Along the bedding are numerous 

 granite bands of various thicknesses, from a small fraction of an 



1 Locality about 200 yards west of Bendoran Cottage. 



