432 EECENT WOEK OF THE GEOLOGICAL SUEVEY 



hornblende-scliist flowing round the harder pebbles of quartz-rock. 

 The latter still preserve their rounded form, but they are traversed 

 by small " step " faults, tending to elongate them in the direction of 

 movement. The original gritty matrix has been converted into a 

 fine micaceous or green chloritic schist, showing exquisite " flow- 

 structure," winding round the elongated pebbles in wavy lines. In 

 short the matrix has been converted into a fine crystalline schist, 

 and but for the presence of the deformed schistose pebbles it would 

 probably be impossible to tell that the schist had a clastic origin. 



No less remarkable is the phenomenon displayed in Corrie Mha- 

 daidh (see fig. 23), where the foliation passes downwards from the 

 Cambrian conglomerate into the underlying gneiss, irrespective of 

 the bedding-planes of the former and the original foliation of the 

 latter. The conglomerate is inclined to the W.jN'.W. at an angle of 

 20°. Along the line of junction it is welded to the old Archaean 

 platform, so that rocks of widely diff'erent geological age practi- 

 cally form one mass. The planes of schistosity in the conglomerate 

 dip to the E.S.E., more or less parallel with the plane of the Ben- 

 More Thrust, and they are continued downwards into the gneiss, the 

 original structures of which have been entirely efi'aced. 



The Cambrian grits, sandstones, and shales have also been pro- 

 foundly affected by these movements. Throughout them all cleavage- 

 planes have been developed, dipping towards the E.S.E., more or 

 less parallel with the plane of the Ben-More Thrust, at an average 

 angle of 45° ; while the original lines of bedding dip towards the 

 W.N.W. Owing to the variable nature of the Cambrian strata, 

 however, the cleavage is very unequally distributed, the beds of 

 coarse grit being less distinctly cleaved, and the planes being more 

 highly inclined than those in the finer sandstones and shaly bands. 

 In fact, there seems to be a constant relation between the inchnation 

 of the cleavage-planes and the texture of the strata. The fine flags 

 and shales behave, so to speak, like lines of weakness, their consti- 

 tuent particles having been drawn out or dragged much further 

 than those of the grits. The planes of schistosity in the grits, flags, 

 and shales form a series of sigmoidal curves, as represented in the 

 accompanying section (fig. 23). 



In addition to the cleavage, new minerals have been developed in 

 the Cambrian strata. Sericite is abundant in the finer bands, so 

 much so, indeed, that they might fitly be termed sericite-schists. At 

 regular intervals too, along finer bands between the grits, lenticular 

 veins of pegmatite occur, more or less parallel with the new schis- 

 tose planes. 



Again, on the slopes of Sgonnan More, the Cambrian flags and 

 shales have been rendered schistose and show minute spots or knots 

 resembling those in the knotted schists. This phenomenon is 

 observable above the outcrop of the Ben-More Thrust-plane. 



Eiually, in the neighbourhood of Little Loch Broom, along the 

 margin of the eastern schists, the Cambrian sandstones have been 

 converted into schists, in which mica has been developed, and 

 wherein the folia show beautiful wavy lines analogous to those in 



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