636 MESSES. J. HOENE AND B. GEEENLT ON [Nov. 1896, 



II. KlEKTOMY TO AEMADALE. 



The various types of crystalline schists with which the granitic 

 rocks are associated in this area may be grouped as follows : — 



1. Granulitic schists or gneiss. 



2. Biotite-schists and gneiss. 



3. Granular gneiss. 



4. Hornblende- gneiss or schist. 



5. Cipolin group (crystalline limestones containing silicates). 



The members of the first two groups display in a remarkable 

 degree the introduction of granitic materials in the form of granitoid 

 folia; thus giving rise to a series of complex gneisses, composed 

 partly of granulitic and partly of granitic constituents. The 

 evidence in the area between Kirktomy and Armadale seems to 

 point to the conclusion that these constructive processes operated 

 after the formation of certain granulitic schists allied to the type 

 of the ' Moine ' schists, and yet the series of complex gneisses 

 recalls some of the features of the Lewisian gneiss between Cape 

 Wrath and Laxford. 



The granite occurs in the form of branching sills, veins, and 

 minute folia, penetrating the schists and gneiss along the planes of 

 foliation, and in places it merges into massive pegmatite. It is 

 usually foliated, the foliation being parallel to that of the schists, 

 though in some instances it is clearly transgressive. 



The essential constituents of the granitoid rocks are orthoclase, 

 oligoclase, quartz, and biotite. A specimen of gneissose granite, 

 taken from the shore at the edge of the outlier of Old Eed Sand- 

 stone, \ mile north of Kirktomy, shows under the microscope 

 orthoclase, oligoclase, quartz, and biotite, with apatite and zircon as 

 accessories. 1 Both felspars occur as allotriomorphic grains, but 

 there are occasional signs that oligoclase may be idiomorphic with 

 respect to an untwinned felspar which is presumably orthoclase. 

 Here and there indications of a micropegmatitic intergrowth of 

 quartz and felspar may be observed. The biotite does not occur as 

 a rule in the form of detached plates, but usually in aggregates of 

 several individuals which mutually interfere with each other. In 

 a specimen of granitoid gneiss between Kirktomy Point and Geodh na 

 Muice muscovite occurs, though not in any great abundance, 

 together with biotite, orthoclase, oligoclase, and quartz. These 

 foliated granites and granitic gneisses are well displayed in the 

 massive form between Kirktomy Point and Pollsain, about | mile 

 east of the headland. 



The granitoid folia, alternating with folia of granulitic schists 

 and biotite-gneiss, may be studied near Kirktomy Point and about 

 a mile to the east near Poulouriscaig. Their constituents resemble 

 those of the larger veins and sills, with the exception that biotite 



1 Microscopic sections of rocks from the Kirktomy area have been examined 

 by Mr. J. J. H. Teall, M.A., F.R.S., who supplied notes on the various rock- 

 specimens and sections. 



