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EECElfT WORK OF THE GEOLOGICAL STTEVET 



the effects of mechanical movements, which, along the same line of 

 strike, merge into a disruption-line. Hence it follows that a zone 

 or belt of gneiss with newer foliation trending W.N.W. may cease or 

 disappear, and be replaced along the same line of strike by contorted 

 gneiss with both the first and second lines of schistosity. (Canisp 

 deer-forest, hills east of Scourie.) 



Pig. 5. — Diagram showing Double Foliation in Archcean Gneiss. 

 (About nat. size.) 



This contortion and double foliation of the gneiss are charac- 

 teristic of the area between Ben Auskaird and Loch Laxford, the 

 general strike of the imperfect second foliation being from 8° to 

 20° S. of E. and N. of W. 



A careful examination of the region near Claisfearn, north of 

 Scourie, points to the conclusion that the folding and contortion of 

 the original gneiss were subsequent to the injection of the basic dykes 

 already described. It seems also pretty clear that the reconstruc- 

 tion of the gneiss in that region has taken place more or less along 

 the old foliation-planes. Where this reconstruction has been 

 carried so far as to involve the complete recrystallization of the 

 original ingredients, then the gneiss may be regarded as practically 

 a new rock. Just as the Silurian quartzites have been crystallized 

 and converted into quartz-schists, frequently along the old bedding- 

 planes, by movements later than Lower Silurian time, even so has 

 the original Archaean gneiss undergone reconstruction along the old 

 planes of schistosity. 



Prom the evidence now adduced it is apparent that, owing to the 

 effects of the various systems of movements here described, the 

 Archaean gneiss possessing the first foliation has undergone con- 

 siderable modification over extensive areas in the west of Sutherland. 

 Its gentle arches and troughs, striking N.E. and S.W., have given 

 place to sharp folds trending N.W., W.N.W., or E. and W., in 

 harmony with the two great systems of disruption-lines. In places 



