IN THE NORTH-WEST HIGHLANDS OF SCOTLAND. 393 



parallel lines or " striping " indicating the direction of movement 

 are usually inclined at angles varying from 15° to 25° to the 

 horizon. It is also observable that the north wall of the dyke has 

 in most cases advanced further to the west than the south wall. 



An important feature connected with the metamorphosis of the 

 diorite into hornblende-schist is the occurrence of segregations of 

 vitreous quartz, varying in width from a few inches to several yards. 

 When best developed the direction of the segregation-veins usually 

 coincides with that of the foliation of the schist. 



In the neighbourhood of Loch Grlencoul thin veins of mica-schist 

 traverse the gneiss, which are believed to represent in a foliated 

 form the dykes of microcline-mica rock near Loch Glendhu. 



The result of these movements trending N.W. on the dykes of 

 peridotite and palaeopicrite has been to convert them, either wholly 

 or in part, into soft talcose schists which can be easily cut with a 

 penknife, the direction of the foliation being determined by the 

 lines of shearing. 



The veins and belts of granite have been changed by the same 

 series of movements into granitoid gneiss, the general trend of the 

 foliation running W.N.W. Of special interest is the appearance of 

 massive pegmatites in connexion with these intrusions. From 

 their mineralogical character there can be no doubt that the 

 constituents have been mainly, if not wholly, derived from the 

 granite. They may occur in the heart of the bands of granitoid 

 gneiss, or the former may run parallel with the latter for long 

 distances, and in some cases portions of the dykes have been 

 completely isolated by the pegmatites. Occasionally the latter 

 have been sheared with the granitic dykes in which they occur, but 

 in such instances the shearing of the pegmatites was subsequent 

 to the first foliation of the granitic intrusions; for there is clear 

 evidence to show that the latter were subjected to a second series of 

 movements, resulting in a modification of the first foliation. Some 

 of the quartz-veins in the hornblende-schists have been similarly 

 afl'ected by this later series of movements. 



The lines of movement trending E. and W. are either vertical or 

 nearly so. When one of these typical thrusts crosses the path of a 

 dolerite-dyke running W.N.W. or N.W., the dyke is gradually 

 deflected from its normal course till it coincides with the line of 

 thrust. On leaving it, the dyke resumes its natural trend. In 

 some of the more striking examples the dykes are wrenched out of 

 their normal course for nearly a mile (jST. of E. of Ben Strome). 



Where the gradual deflection takes place, the diorite begins to 

 lose its granular character and eventually passes into a black, 

 compact, flinty rock in the line of crush ; or the dyke is completely 

 recrystallized and converted into a fine hornblende-schist. These 

 changes are accompanied by a remarkable attenuation of the basic 

 intrusions, for in some cases dykes measuring 50 or 60 yards across 

 shrink into bands 4 feet wide in the crush-lines. They are not 

 reduced to the same uniform width, however, as they frequently 

 form eye-shaped masses, completely isolated from each other and 



