Vol. 60.] METAMOEPHISM IN THE LOCH-LOMOND DISTRICT. -3 



in Hoosac Mountain, 1 calls attention to the strings and lenticles 

 of quartz developed along the bedding-planes of the albite-schist, 

 as evidence of a higher percentage of silica in the rock than would 

 be met with in a true phyllite. 



In the Survey Memoir on the 'Geology of Cowal,' also. Mr. C. T. 

 Clough suggests the possibility of the development of albite-gneisses 

 from phyllites ; and two analyses (op. cit. p. 39) were made from 

 selected specimens — one of phyllite, the other of albite-gneiss, to 

 see whether these rocks were similar in chemical composition. 

 These analyses are tabulated below. 



I. 



Per cent. 



Si(X 43-3 



TiO" 2 1-2 



Al.,0, 26-2 



FeO I l 136 



MnO not estimated 



CaO 0-5 



MgO 38 



KX> 4-6 



Na o 1-8 



H 2 1 



C0 2 j 4o 



P 2 0- not estimated 



S not estimated 



II. 



III. 



IV. 



Per cent. 



Per cent. 



Per cent, 



634 



65-11 



7722 



trace 



0-83 



0-59 



18-1 



15-78 



10-07 



6*7 



6-49 



4-02 



not est. 



0-24 



0-30 



0-9 



1-34 



1-10 



19 



1-95 



117 



3-2 



3-97 



2-65 



32 



2 49 



2-65 



■>-o 



1-41 



0-36 



_ o 



039 



0-32 



not est. 



0-25 



014 



not est. ' 



044 





Totals 99-5 100-2 100-39 100-59 



As the iron in I & II was estimated as Fe 2 3 . and FeO was not estimated, 

 the total iron in III & IY is given as Fe.-,0 3 for the sake of comparison. 



The percentages 4 - 5 & 28 in I & II respectively were ' loss on ignition,' and 

 are given as H.,0 & C0 o bracketted ; this loss may also include a percentage of 

 sulphur. 



I. Green phvllite from Blairmore (Cowal), } i i u vr t t tt t q „"!1 

 tt 4iu*. i- * * en i -d n i\ > analysed bv Mr. J.J. 14. leail. 



II. Albite-schist irom fetuck Burn ( Cowal), J J J 



III. Albite-gneiss from Rudha Ban, 1 , j u -r» n- t> n i 

 »,; i.. B .. - x» ii -n ii ^ analysed bv Dr. \\ . Pollard. 

 I\ . Schistose grit from Rudha Dubh, J J 



For the ; Explanation of Sheet 38 ' by the Geological Survey, 

 two analyses have also been made by Dr. W. Pollard : one of a typical 

 albite-gneiss from Rudha Ban ; the other of the coarsest and most 

 siliceous grit that could be obtained in the section on the western 

 shore of Loch Lomond, at Rudha Dubh. It must be mentioned 

 here that a finer- grained, less siliceous, and more micaceous speci- 

 men of schistose grit could easily have been selected : but in order 

 that there should be no forcing of the evidence to agree with the 

 conclusions to which I had come previously, I determined to select 

 the verv coarsest and most siliceous irrit that I could find — in fact, 

 what I may call an extreme case of siliceous grit, as compared with 

 an average specimen of albite-gneiss. 



1 Monogr. U.S. Geol. Surv. vol. xxiii (1894) pp. 59 et scqq. 



