184 PETROLOGICAL NOTES ON SOME OF THE ERRATICS 



1863. Actinolite Schist 



Macroscopic Character s. — Very dense grey rock with decided tendency to 

 cleavage. Transverse to the direction of parting a perfect conchoidal fracture is 

 developed. An obscure banding can be noticed. No individual constituents can be 

 recognised. 



Microscopic Characters. — The banding noted in the hand-specimen is very 

 distinct under the microscope. The more coarsely crystalline bands are extremely fine, 

 and the finer ones are crypto- crystalline. The coarser bands have strongly parallel 

 arrangement of the prismatic constituents. Most abundant and conspicuous are 

 prisms of actinolite up to - 2 mm. long and extremely slender. These, together with 

 flakes of light brown mica and longish splinters of quartz, are embedded in a base of 

 quartz and twinned and un twinned felspar, too fine for optical determination. 



In the finer bands actinolite prisms of much larger size (0"8 mm. to 0*2 nun.) are 

 sparsely distributed. In cross- sections of these prisms the trace of the (100) face is 

 predominant and (010) is absent. Sometimes these larger prisms project from the finer 

 into the coarser bands. In the latter the centres of crystallization of the amphibole are 

 much more numerous, and there is a tendency for the formation of feathery aggregates. 



It is possible that this rock is a somewhat altered lightish coloured lamprophyre 

 of very fine grain. The arrangement of the larger actinolite crystals is a little suggestive 

 of this ; but, on the other hand, the habit of this mineral, the character of the mica, and 

 the mode of occurrence of the quartz all point to a metamorphic origin. The rock 

 is very similar to quite a number of others whose metamorphic origin is undoubted. 



1869. Actinolite Schist 



Macroscopic Character s. — Very dense and heavy dark-greenish rock, dis- 

 tinctly banded. Splits parallel with the plane of the bands, but in other directions 

 has a conchoidal fracture. No individual constituents visible. 



Microscopic Characters. — Generally similar to No. 1863, but not so dis- 

 tinctly foliated. It consists essentially of actinolite, quartz, and brownish mica, but 

 contains less quartz than the rock just described. The lepidoblastic ground fabric 

 consists almost entirely of actinolite prisms with a little interstitial quartz. 



There are a few small porphyroblasts of a colourless prismatic mineral with its 

 long axes lying across the schistosity. This may be cyanite; it gives extinction 

 angles up to about 30° from its length, and in optical character, optical sign, optic 

 axial angle, and double refraction, answers to that mineral. The refractive index appears 

 to be somewhat low. 



1855. Actinolite Schist 



Macroscopic Character s. — An extremely fine-grained black rock, finely 

 banded, some of the bands being strongly pyritic. 



Microscopic Character s. — The rock is distinctly banded, the alterations 

 in colour being due to differences in the character of the actinolite in the different 

 bands. The fabric is distinctly lepidoblastic on the whole, the essential constituents 

 being actinolite and colourless base with minor amounts of magnetite, calcite, and 

 greenish mica. In the dark bands the actinolite is very abundant, quite dark green 

 and strongly pleochroic : 



9 colourless ; fj and C dark green. 



