386 EECENT wore: of the geological SrEYEY 



2. The planes of schistosity in the eastern metamorphic schists 

 are not planes of bedding, but planes of shearing and cleavage, 

 along which the rocks have yielded to the lateral crust-pressure. 



3. By the action of this lateral earth-thrust, the Archaean, the 

 Plutonic, and included patches of sedimentarj' rocks have been 

 locally sheared and flattened out into rocks resembling halleflintas, 

 rhyolites, and finely laminated shales. 



4. The eastern metamorphic series of Sutherland and Eoss not 

 only contains Archaean rocks, but also local patches of metamor- 

 phosed Palaeozoic, intrusive, and segregatory rocks, together with 

 local patches of material, probably compounded of all these in 

 different degrees. 



5. The eastern metamorphic series has received its present strike, 

 pseudo-bedding, and its present foliated and mineralogical charac- 

 teristics through the agency of the crust-movements which have 

 operated within the district since Lower Silurian times. 



The stratigraphy of the "West Highlands, he maintained, is of the 

 same character as that described by Heim, in his work on the Alps 

 of Central Switzerland ; while the metamorphic phenomena are 

 identical with those detailed by Lehmann, in his publications on the 

 metamorphic rocks of the Saxon Erzgebirge. 



In 1885 * a valuable paper was published by Mr. Teall " On the 

 Metamorphosis of Dolerite into Hornblende-schist," as displayed by 

 two more or less parallel dykes in the Archaean gneiss, near the 

 village of Scourie, in Sutherlandshire. From a careful examination 

 of the phenomena presented by the dykes in the field and by micro- 

 scopic sections of the rocks, he concluded (1) that the hornblende- 

 schist has been developed from a dolerite by causes operating after 

 the consolidation of the dolerite, and that the metamorphosis has 

 been accompanied by a molecular rearrangement of the augite and 

 felspar : (2) that the molecular rearrangement has in certain cases 

 taken place without the development of foliation; (3) that the 

 plasticity which has led to the development of foliation is that due 

 to high pressures at ordinary temperatures. These deductions are 

 of far-reaching importance in interpreting many of the phenomena 

 of the Archsean rocks. 



The Geological Survey began the detailed mapping of the Xorth- 

 west Highlands in 1883, by tracing out the structure of the lime- 

 stone district of Durness and Eriboll in the north of Sutherland. 

 Since that time the work has made considerable progress, chieflv 

 along the belt of extraordinarily complicated ground from Eriboll 

 southwards through Assynt to Dundonald — a distance of fifty-five 

 miles. To the west of that belt the tract between Cape TTrath and 

 Lochinver, mainly occupied by Archaean rocks, has been surveyed. 

 To the east, large districts of the eastern or newer schists between 

 Tongue and Loch Broom have also been examined in detail. A 

 large mass of evidence bearing on the nature and extent of the 

 ancient terrestrial movements in the Xorth-west Highlands, and 

 throwing much light on the origin of the schistose structure in 

 * Quart. Journ. Geol. Soc. ral. xli. p. 133. 



