190 Canadian Record of Science. 



dorite and some sections of the same which he submitted to 

 me for examination were found to be composed of a mul- 

 titude of small grains, none of which were twinned." 



An examination was likewise made of well twinned pla- 

 gioclase from two other localities. The first was from a 

 hand-specimen of a typical anorthosite which occurs five 

 miles north-west of Ste. Adele in the Morin district. Its 

 specific gravity was between 2.65 and 2.6*7, and it had 

 therefore, also, the composition of an acid labradorite, a 

 fact confirmed by the values of the extinction angles 

 measured on a small fragment separated by means of 

 Thoulet's solution. The second was from the village of Ste. 

 Adele itself, which lies near the southern edge of the 

 Morin area. Here the anorthosite has porphyritically dis- 

 tributed through it large plagioclase crystals which some- 

 times are not less than four inches long. These had the 

 following extinction angles : on ooP oo (010) 24j° to 

 26°, on O P (001) = 6°. An analysis of the bluish opal- 

 escent plagioclase from the Morin district will be found in 

 the table of analyses given at the end of this paper ; here 

 again the feldspar is a labradorite. 



The plagioclase of the anorthosite from these six different 

 localities is therefore in all cases labradorite, and there is 

 every reason to believe that the feldspar throughout the 

 whole area belongs to this variety. Although it was gen- 

 erally quite fresh, a partial decomposition was observed in 

 one or two cases where it was changed into a mixture of 

 calcite, epidote and zoisite as mentioned in the description 

 of these minerals. 



This occurrence was found in the village of New Glas- 

 gow, where a peculiar variety of rock having a saussuritic 

 habitus was also observed. This latter was quite a local 

 occurrence connected with the small zones of disturbance 

 which here run through the anorthosite. We see in thin 

 slices that this plagioclase (the rock is composed almost 

 entirely of this mineral mixed with a few small grains of 

 iron ore) has suffered a peculiar alteration. The product of 

 decomposition is a mineral mostly of fibrous structure which 



