184 DR. C. E. TILLEr ON THE PETROLOGY OF [vol. lxxix r 



The norm of this rock is : — 



Per cent. 



Orthoclase 2-78 



Albite 27-25 



Anorthite 26-70 



Per cent- 



Hypersthene 13-92 



Olivine 4-62 



Magnetite 6-03 



Diopside 12-26 I Ilmenite 3-50 



and the mode, as in part determined : — 



Per cent. 



Per cent. 



Titanite 4-5 



Albite 30-0 



Chlorite "} 



Epidote >• 65'5 



Hornblende ) 



Green Schists showing porphyrohlasts of albite in a chlorite- 

 epidote ground-mass are not uncommon. On weathered faces the 

 albite-crystals stand out from the rock, imparting to it a knotted 

 appearance. A good example of a rock of this type from Leek 

 Cove was studied. From the type already described this rock differs 

 mineralogieally in the presence of a considerable amount of white 

 mica, and its association with narrow bands of undoubted sediment 

 leads to the conclusion that the rock is a metamorphosed basic 

 ash. 



The constituents are chlorite, epidote, albite, titanite, blue-green, 

 fibres of amphibole especially associated with chlorite, muscovite, 

 and magnetite giving place to haematite. Some bands of this rock 

 are very rich in muscovite associated with chlorite. Quartz is 

 absent. 



The porphyrohlasts of albite range in size up to 1*5 mm., are 

 occasionally twinned, and cleavages are usually well developed. 

 They commonly show a poikiloblastic texture, due to the presence 

 of fibres of amphibole and elongated crystals of a ferriferous 

 epidote. These are characteristically arranged in parallel, but are 

 not necessarily parallel to the longer axes of the porphyrohlasts of 

 albite. Except for the inclusions above noted, the albite-grains 

 are water-clear. A rock of this character, except that muscovite 

 is absent, is described from Inner Hope by Sir Jethro Teall in 

 Ussher's memoir. 1 



The rocks so far described have been completely free from a 

 carbonate mineral. Usually, however, this mineral (calcite) is 

 common among many of the Green Schists of this type. The 

 calcite in some cases may rank as an important constituent, and 

 there is every reason to believe that it has crystallized as such 

 during the metamorphism of the rocks. It is intimately inter- 

 grown with albite, and shows multiple twinning of the usual type. 

 Chlorite is the common inclusion, but enclosures are not abundant. 

 In accordance with its position in the crystalloblastic series, the 

 calcite is moulded on to the more idioblastic albite. In the true 



1 ' The Geology of the Country around Kingsbridge ' Mem. Geol. Surv, 

 1904, P ; 61. 



