42 STKATIGRAPHICAL GEOLOGY 



Clough and Crampton 5 from a study of the aureole or /one of 

 contact-metamorphism round the gneissic granite of Cam Chuin- 

 neag in Ross-shire. Within this zone the Moine sediment was 

 altered and indurated before the incidence of the dynamic meta- 

 morphism, the consequence being that the beds have to a large 

 extent escaped the effects of that metamorphism and can be recog- 

 nised as hornfelses formed from the alteration of ordinary sandstone 

 and shales 



The hornfelses occur where a sandy shale was in contact with 

 the granite ; it is now a hard and splintery rock, and where least 

 affected by subsequent shearing it shows both a clastic structure 

 and the original lamination. The more quartzose bands often 

 contain minute pebbles of rounded quartz ; and " On the surfaces of 

 certain layers there are markings strongly suggestive of sun-cracks 

 and ripple-marks, and others which may possibly represent worm- 

 tubes." Moreover, the beds lie with gentle inclinations, and they 

 dip at right angles to the general direction of the foliation-bedding 

 or shearing of the neighbouring schists. Lastly, intermediate stages 

 between the typical hornfels and the foliated schists have been 

 observed ; and it is clear that all the rocks were solid at the time 

 when the pressure-foliation was induced, the granite being then 

 converted into a gneiss and the shales into mica-schists, while the 

 rocks of the indurated aureole were more resistant and are con- 

 sequently much less altered. 



The Moine schists and the underlying Hebridean rocks have 

 now a common foliation which has obscured that which previously 

 existed in the older series : they have also a common flexion and 

 plication, the rock-masses being folded into a complex system of 

 isoclines, the prevalent strike of which is from S.S.W. to N.N.E., 

 though they vary in direction round the inliers of Hebridean gneiss. 



The above description applies more particularly to the areas 

 north and west of the Great Caledonian Glen. East of the faults 

 which run along this glen the country is occupied by large tracts 

 of similar quartzo-felspathic schists, which, however, differ in being 

 more persistently flaggy, the layers being alternately more and less 

 micaceous. Hence the name Eilde Flags has recently been used as 

 a special designation of this portion or facies of the Moine schists. 6 



We now pass to the equally large area of the Central Highlands, 

 which extends across the centre of Scotland from parts of Aberdeen 

 and Kincardine on the N.E. through Perthshire and Argyllshire 

 to the coasts of Cantire and Islay. This area is occupied mainly 

 by three different kinds of rocks, first and principally by a series 

 of metamorphosed sediments comprising quartzites, phyllites, and 

 limestones, secondly of small tracts of Eilde flags, and thirdly of 



