Alnoitie Rocks at Isle Cadieux, Que. 11 



Inclusions. 



Inclusions in the igneous mass are decidedly rare ; not 

 even locally was any facies observed that remotely 

 approached a breccia. 10 A few inclusions were seen, 

 however, and it was possible to obtain some of these for 

 sectioning. They were found to be of three kinds: (a) 

 large augite crystals, (b) an aplitic rock, (c) a sodic 

 syenite. 



The augite crystals are fairly numerous at the north- 

 ern margin of the mass as exposed, and stand out as 

 knobs about an inch in diameter on the weathered surface. 

 Peripheral alteration of the crystals by the magma is 

 often to be seen even in the hand specimens, the core being 

 of black glassy appearance and the border dull. The 

 optical properties of the crystals show them to be iden- 

 tical with the augite of the rock itself. This fact sug- 

 gests that they may be phenocrysts rather than inclusions 

 but their general appearance is rather that of cognate 

 xenocrysts. 



The inclusion of an aplitic rock that was broken out for 

 study was found to be of a highly siliceous type, probably 

 a fragment of a fine-grained dike. It is very rich in 

 quartz; the feldspar, evidently an alkaline one, is much 

 kaolinized, and these make up practically the whole rock. 

 There is, however, a little segiritic pyroxene "in minute 

 prisms, frequently forming matted masses," 11 with green 

 to yellow pleochroic colors, small extinction angle, and 

 negative elongation. A few grains of zircon were 

 observed also. The quartz of this rock shows under the 

 microscope a marked development of an imperfect cleav- 

 age that breaks it up into roughly rectangular pieces. 

 The presence of this cleavage or cracking is probably to 

 be taken as evidence that the inclusion has been heated 

 above 575° by immersion in the alnoite material, the 

 quartz therefore passing through the a-p quartz inversion 

 point. 12 Presumably it was not heated to 870°, for there 

 is no suggestion of a change to tridymite. In the course 



10 The interior portions of some of the masses described by Harvie (op. 

 eit. p. 256) are often nearly free from inclusions. 



11 The segirite of the tinguaite of this province is so described by 'Neill, 

 Geol. Surv. Can. Mem., 43, p. 60, 1914. 



13 Wright and Larsen, Quartz as a geologic thermometer, this Journal, 27, 

 437, 1909. 



