Marshall. — The Kingston Moraine. 389 



(B 104.) Diorite. — An even-grained light-green rock in 

 which the hornblende and feldspar can be distinguished 

 readily. Section : Feldspar twinned on albite and pericline 

 laws. Extinction angle indicates a basic oligoclase or an de- 

 sine. Very slight cloudiness indicates the commencement of 

 decomposition. Hornblende light-green, showing the usual 

 absorption. Quite fresh. Magnetite generally in irregular 

 masses, but occasionally idiomorphic, is common. Apatite 

 needles pierce through the hornblende. 



(B 105.) Diorite. — Light-green rock, with white feldspar 

 crystals and light green hornblende. Not porphyritic in habit. 

 Section : Feldspars all plagioclase and giving extinction angles 

 characteristic of andesine. Albite and pericline twinning com- 

 mon. Amphibole completely fibrous, with irregular termina- 

 tions Light-green in colour and slightly pleochroic. Fibres 

 differ slightly in optical properties, showing a striated appear- 

 ance between crossed nicols. Probably all secondary, the 

 amphibole being actinolite. Magnetite in small grains occurs 

 throughout the section. 



(A 161, 193, 194.) Feldspar Porphyrite. — Dark-green base, 

 with distinct light flesh-coloured phenocrysts of feldspar, of 

 tabular habit. Sections : Feldspar phenocrysts twinned poly- 

 synthetically on albite law and Carlsbad. Maximum extinc- 

 tion angle on sections perpendicular to 010 32°, indicating a 

 feldspar of a rather acid labradorite type. Thickly dusted 

 with decomposition products, which from their high birefrin- 

 gence and colourless nature appear to be muscovite scales. 

 Groundmass consists of feldspar microlites, apparently labra- 

 dorite much decomposed contained in a fine-grained mixture 

 of green amphibole and brown mica. The amphibole shows 

 no crystalline boundaries. It is highly pleochroic in shades 

 of green. Maximum extinction 18° with the cleavage. Struc- 

 ture fibrous. Mica in very small plates. No distinct out- 

 line. From their arrangement it is almost certain that the 

 last two minerals are secondary. 



(A 187.) Porphyrite. — A black rock with weathered sur- 

 face, covered with rounded hard resistant knobs. Generally 

 similar to the groundmass of A 161. Section : Feldspar fairly 

 large grains, penetrated through and through with epidote 

 needles. Optical properties can still be distinguished in some 

 of the crystals, and prove them to be labradorite. Amphibole, 

 where original, very light-green, with ordinary absorption and 

 twinning ; where secondary, bright-green and actinolitic. 

 Brown mica in small plates, probably secondary. Magnetite 

 generally scattered through the rock. 



(A 156.) Forellcnstcin. — Light-grey rock, with undecom- 

 posed feldspar showing bright cleavage planes. Not porphy- 

 ritic. Section : Very fresh feldspar without idiomorphic 



