Vol. 59.] XOER1DONIAN, ETC. OF THE TSLE OF REM. 197 



is to a great extent lost, and the intrusions, extending farther 

 northward, entirely cut out the overthrust belt. 



The curved course of the outcrop of the overthrust surface, 

 following the outward slope of the high ground, permits us to 

 regard that surface as having on the whole a gentle inclination 

 towards the south-east. Regarding this course in detail, however, 

 and in relation to the minor features of the ground, we see that 

 the surface must be in reality greatly warped, and has in some 

 places a rather high inclination to the horizontal. Along a great 

 part of its length the outcrop of the overthrust runs at altitudes 

 between 1000 and 400 feet, but in the south-east of the island 

 it rises considerably higher inland, and at the same time comes 

 down to sea-level at the coast. This is seen on Beinn nan Stac, 

 where the average inclination of the overthrust surface does not 

 differ much from the seaward slope of the hill (see section, fig. 4, 

 p. 202). 



The outcrop of the overthrust surface is easily mapped, for the 

 effect of the displacement is, in general, to cause the shales of the 

 lower group to rest on the sandstones of the upper. The overlying 

 displaced rocks have suffered very great mechanicaldisturbance, as is 

 shown by their high and variable dips and violent contortion, and 

 in some places by brecciation on an extensive scale. The relatively- 

 unmoved strata below are much less disturbed, sometimes not more 

 so than in the north of the island ; but along parts of the line they 

 have an altered and steeper dip, and in certain places they are brec- 

 ciated. The voluminous intrusions of peridotite, gabbro, granite, 

 etc., have given rise to considerable metamorphism of the thermal 

 type, superposed upon the dynamic effects. The results of such 

 metamorphism are more often conspicuous in the displaced strata 

 than in those below the overthrust ; but this is only a necessary 

 consequence of the overlying position of the igneous rock-masses. 

 There is no essential connection between the dynamic and the 

 thermal transformations, and the latter seem to stand always in 

 direct relation to the proximity of the large plutonic intrusions. 

 The phenomena of metamorphism of the crush-breccias and numerous 

 other circumstances enable us to affirm that the thermal meta- 

 morphism was subsequent to the dynamic, and its distribution 

 warrants us in ascribing it, in the main if not wholly, to the Tertiary 

 intrusions. In making this statement we ought to reserve the case 

 of certain gneissic rocks, found above, and sometimes below, the 

 overthrust surface, which will be discussed farther on. 



The belt of displaced rocks will now be considered in more 

 detail, beginning at the centre of the island. To the west the 

 overthrust strata are cut out (as has been remarked) by the igneous 

 intrusions, which in this part assume something of the boss-like 

 habit. The overthrust is first met with a little to the east of the 

 north-and-south valley in which lies Loch Sgathaig or the Long Loch. 

 The main line of the displacement follows here a very sinuous course, 

 though with a general easterly direction, and it is interrupted in 



