, 9 2 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1 894, 



fine, micaceous, chloritic schist showing exquisite ' flow-structure,' 

 winding round the elongated pebbles in wavy lines — in fact the 

 matrix has been converted into a fine crystalline schist. In the 

 grits, etc., of this formation cleavage-planes have been developed, 

 dipping in a direction opposite to that of the original bedding, and 

 more or less parallel with the plane of the maximum thrust. As 

 the materials differ in their powers of resistance the planes of 

 schistosity, in some cases, form a series of sigmoidal curves. Lenti- 

 cular veins of pegmatite occur more or less parallel with the new 

 schistose planes, whilst sericite is found to be abundant in the finer 

 bands. 



The various members of the Cambrian series underlying the 

 Glencoul thrust-plane show little alteration, even when they have 

 been piled on each other by minor and major thrusts, but above the 

 Ben More thrust-plane a greater amount of alteration takes place, 

 the steps in which may be traced until such a bed as the ' Serpulite- 

 grit ' becomes a quartz-schist in which ' serpulites ' are no longer 

 visible : meanwhile the limestone becomes crystalline. As regards 

 the post-Cambrian metamorphism of the intrusive igneous rocks, 

 there is a certain progressive change from west to east. Thus, 

 sheets of felsite injected along the bedding-planes of the basal 

 quartzites have been converted into soft sericite-schists ; and in 

 another place a felsite-dyke on the same horizon has had cleavage 

 developed parallel to the plane of the principal thrust, whilst but 

 little alteration is noticed in the quartzite itself. Where the altera- 

 tion is extensive, as in the neighbourhood of the Moine thrust-plane, 

 the various igneous bands lose their distinctive characters : the 

 fine-grained diorites in the limestones are represented by green 

 hornblende-schists and chlorite-schists ; the noncrystalline rocks 

 with porphyritic felspars appear as bands of ' augen-gneiss ' and 

 * augen-schist ' ; and finally, along a line of powerful thrust in the 

 great granitoid sheet east of Loch Borolan, there is a belt of ' augen- 

 gneiss' with pyroxenes, which, existing originally as porphyritic 

 crystals, now appear as ' eyes ' in the foliated rock. 



As rightly pointed out by Messrs. Peach and Home, there is much 

 valuable information to be gathered from a study of this progressive 

 metamorphism. Amongst other inductions it is obvious that the 

 crystalline rocks, where they occur in thin sheets, become schistose 

 more readily than the ordinary clastic rocks. As might be expected, 

 too, the Torridonian sandstones and shales are more easily cleaved 

 than the Cambrian quartzites. In fact, when we bear in mind 



