Vol. 52.] FOLIATED GRANITES IN EASTERN SUTHERLAND. 643 



into Group 2 in the same way as that does into Group 1. From 

 this, and from the abundance of sillimanite, it seems reasonable to 

 infer that it also is of sedimentary origin. Seams of quartz-schist 

 occur within it. 



Granites occur in all these rocks as veins and sills. Those in the 

 quartz-schist are red pegmatitic-looking veins, composed of oligoclase, 

 microcline, quartz, and muscovite ; while those in the other schists 

 about Suisgill contain biotite and very little muscovite, their felspar 

 being (so far as determined) oligoclase, and sometimes probably 

 natron-orthose. All these rocks have sharply-defined margins, and 

 are hardly ever foliated. 



Groups 1, 2, 3 follow in order north-westward from Kildonan, 

 till, about Borrobol, a large mass of Group 2 comes in again. When 

 we approach the north-western margin of this, we find that a change 

 has set in. The granites, which hitherto have not been very 

 numerous, now appear in great numbers, and ' injected lit par lit,' 

 as well as along old faults, now completely healed up by interlocking 

 crystallization, just as on the coast of Portskerry, forming with the 

 granulitic schists a ' synthetic gneiss.' A little distance farther on, 

 however, we leave the granulitic type, and enter a tract of coarse, 

 wavy, highly crystalline gneiss, like that of Bowside near the 

 northern coast. It is composed of quartz, felspar, and very black 

 mica (often olive-green by transmitted light). The felspars are 

 large and well striated. They are chiefly oligoclase, but albite and 

 orthoclase also occur. Garnet is not uncommon, and sillimanite 

 occurs locally, sometimes most beautifully crystallized. 1 



In spite of the coarsely crystalline texture of this rock, especially 

 the large size of its beautiful striated felspars, there is a general 

 resemblance in structure to the wavy mica-schists of Suisgill, and 

 in places it could not be distinguished from these ; and I am inclined 

 to believe that, although it may contain other material as well 

 which has not yet been separated, nevertheless the greater part of 

 it is the Suisgill mica-schist in a more highly crystalline condition. 

 It occupies a very large area, extending, with only one interruption 

 of 1| mile of granulitic gneiss, across the strike, all the way to the 

 Naver. 



Now it is in this rock that the most wonderful granitic intrusions 

 occur. The phenomena so clearly seen in the cliff's of Strathy Point 

 are here repeated in their highest intensity. Great sills of granitoid 

 rocks, often a mile in width, range for miles along the country, and 

 every gradation exists between these and the very thinnest bands 

 and seams. 



The felspars of these granites are in all cases so far determined 

 oligoclase, often inclining to andesine, except certain porphyritic 

 crystals of rather rare occurrence, which are natron-orthose. Albite 

 and microcline occur in some small pegmatites. The large porphyritic 

 crystals only are idiomorphic, the rest having the form called by 



1 These and other minerals were determined during field-work from crushed 

 fragments under the microscope ; laboratory tests being used afterwards, for 

 confirmation in doubtful cases. 



