622 REPORT— 1901. 



1. The compressed mass tends to find relief alont^ a series of gently inclined 

 thrust-planes, which dip towards the side from which pressure is exerted. 



2. After a certain amount of heaping up along a series of minor thrust-planes, 

 the heaped-up mass tends to rise and ride forward bodily along major thrust- 

 planes. 



3. The front portion of a mass being pushed along a thrust-plane tends to bend 

 over and curve under the back portion. 



4. A thrust-plane below may pass into an anticline above ; and a major thrust- 

 plane above may and probably always does originate in a fold below. 



Now these important experiments confirm the conclusion reached by the 

 Geological Survey from a study of the phenomena in the field, viz., that under 

 the influence of horizontal compression or earth-creep the rocks in that region 

 behaved like brittle rigid bodies which snapped acrops, were piled up and driven 

 westwards in successive slices. But, further, these displacements were accompanied 

 by diflerential movement of the materials which resulted in the development of 

 new structures. These phenomena culminate along the belt of rocks in immediate 

 association with the Moine Thrust, where the outcrop of that thrust lies to the 

 east of a broad belt of displaced materials. There, Lewisian gneiss, Torridon 

 Sandstone, and Cambrian quartzite are sheared and rolled out, presenting new 

 divisional planes parallel with that of the Moine Thrust. The Lewisian gneiss 

 shades into flaser gneiss and schist, and ultimately passes iu<oa banded rock like a 

 platy schist. The pegmatites show fluxion structure with felspar ' eyes ' like 

 that of the rhyolites. At intervals in these zones of highly sheared rocks, pha- 

 coidal masses of Lewisian gneiss appear, in which the pre-Torridonian structures 

 are not wholly efl^aced. The sills of camptonite and felsite intrusive in the Cam- 

 brian rocks become schistose and together with the sediments in which they occur 

 appear in a lenticular form. All these mylonised rocks show a characteristic 

 striping on the divisional planes, due to orientation of the constituents in the 

 direction of movement. 



Still more important evidence in relation to the question of regional metamor- 

 phism is furnished by the Torridon Sandstone. In the case of the basal con- 

 glomerate the pebbles have been flattened and elongated, and a fine wavy structure 

 has been developed in the matrix. In the district of Ben More, Assynt planes of 

 schistosity, more or less parallel with the planes of the Ben More Thrust, pass 

 downwards from the Torridon conglomerate into the underlying gneiss. Both 

 have a common foliation irrespective of the unconformability between them. 

 Again, along the great inversion .south of Stromeferry, foliation has been developed 

 in the Torridon conglomerate and overlying Lewisian gneiss, parallel to the plane 

 of the Moine Thrust. The Torridon grits and sandstones south of Kinlochewe 

 and between Kishorn and Loch Alsh are similarly afiected by the post-Cambrian 

 movements. Mr. Teall has shown that the quartz grains have been drawn out 

 into lenticles and into thin folia that wind round ' eyes ' of felspar. A secondary 

 crypto-ci-ystalline material has been produced, sericitic mica appears in the divi- 

 sional planes, and in some instances biotite is developed. In short, he concludes 

 that in these deformed Torridonian sediments there is an approximation to the 

 crystalline schists of the Moine type. The stratigraphical horizon of these rocks 

 can be clearly proved. The subdivisions of the Torridon Sandstone have been 

 recognised in those displaced masses which lie to the east of the Kishorn Thrust 

 and to the west of the Moine Thrust. It is worthy of note also that in the belt 

 of highly sheared gneiss south of Stromeferry that comes between the Torridonian 

 inversion in the west and the Moine Thrust on the east Mr. Peach has found 

 folded and faulted inliers of the basal division of the Torridon Sandstone that have 

 a striking resemblance to typical Moine schists. 



Regarding the age of these post- Cambrian movements, it is obvious that they 

 must be later than the Cambrian limestone and older than the Old Red Sandstone, 

 for the basal conglomerates of the latter rest unconformably on the eastern schists 

 and contain pebbles of basal quartzite, pipe-rock, limestone, and dolomite derived 

 from the Cambrian rocks of the North-west Highlands. 



East of the Moine Thrust or great line of displacement extending from Eriboll 



