part 2] THE METAMORPHOSED ROCKS OP THE START AREA. 199 



indications that common hornblende and muscovite are infrequent 

 associations in rocks of metamorphic origin. Among those rocks 

 in which hornblende and white mica are known as characteristic 

 associates, the amphibole is in many cases a glaucophane, or the 

 white mica has been proved to be the sodic paragonite. 1 



With increasing metamorphism in the composite rocks of the 

 Start area, garnet appears after chlorite, and takes the place of 

 the hornblende in the true Green Schists. 



The mineralogical constitution of the three groups of rocks in 

 equivalent grades of metamorphism [may be compared in the 

 following synopsis : — 



Mica-Schists. 



Green Schists. 



Schists of composite 

 origin. 





Chlorite. 





Chlorite. 





Epidote. 





Muscovite. 





Albite. 





Albite. 



Quartz. 



Muscovite. 



J Hornblende. 

 (_ Titanite. 



} 



Quartz. 



J Epidote. 1 

 t Titanite. J 



Chlorite. 









[Albite.] 



Hornblende. 









Epidote. 





Garnet. 





Albite. 









f Chlorite. 1 

 [ Titanite. J 













In the succeeding stages which are not represented in the Start 

 Group, biotite would presumably appear in the mica-schists and 

 composite rocks, and hornblende as a characteristic constituent of 

 the latter class would appear still later. Evidence for this is 

 supplied in the metamorphosed green beds of the Highlands, and in 

 the metamorphosed sediments of the Stavanger district of Norway. 



VIII. Comparison with other Green Schist Areas. 



The classical work of K. A. Lossen 2 on the metamorphosed 

 diabases of the Eastern Harz, and of G. H. Williams 3 on the 

 greenstone schists of the Lake Superior region, has led the way to" 



1 See especially U. Grubenmann, ' Ueber einige Schweizerische Glaukophan- 

 Gesteine ' Festschrift H. Eosenbusch, 1906, p. 11 ; id. ' Die Kristallinen 

 Schiefer ' 1910, p. 201 ; T. J. Woyno, Neues Jahrb. Beilage-Band xxxiii (1911) 

 pp. 180 et seqq. ; and E. Greenly, ' The Geology of Anglesey ' Mem. Geol. 

 Surv. vol. i (1919) p. 117. 



2 ' Erlliuterrmgen zur Geologischen Specialkarte von Preussen & den 

 Thiiringischen Staaten ' 1882-83 (Pansfelde & Wippra sheets) ; and id. Jahrb. 

 K. Preuss. Geol. Landesanst. 1883. 



3 Bull. U.S. Geol. Surv. No. 62, 1890. 



P2 



