Granites from Britisli Columbia, etc. 347 



though this may be due in part to the fact that these 

 crystals are very small. 



In two or three cases twin crystals of allanite were found, 

 the twinning line probably being coPoj f in one case extinc- 

 tions of 23° and 27° respectively on either side of the 

 twinning line were observed, but none of the crystals were 

 cut quite parallel to the clinopinacoid. The epidote, when 

 associated with these allanites, has crystallized around 

 them, sometimes enveloping them completely, but at other 

 times only partially, forming what is generally a very 

 irregular border. The allanite and epidote are probably 

 intergrown in parallel position, but no section was found 

 so cut that this could be actually proved. The mode of 

 occurrence of these two minerals is seen in the accompany- 

 ing cut (Fig. 1) in the upper left hand division, the epidote 

 being represented in outline, while the allanite is black. 

 This association of epidote and allanite has already been 

 described from a number of localities. 1 



The epidote is remarkable, not only as occurring in very 

 considerable amount in the granite, but also from its mode 

 of occurrence. It is evident at the first glance that it does 

 not result from the decomposition of the plagioclase or 

 other constituents of the rock, as is frequently the case in 

 much decomposed igneous rocks, since it occurs in large 

 well defined crystals, these however seldom have a 

 perfect form but possess a very peculiar eaten or corroded 

 appearance, being traversed by little irregular canals and 

 arms of another colourless mineral with much lower index of 

 refraction. These arms are in many cases, too small to enable 

 their character to be determined, but on careful examina- 



1 Becker, Ewald. — "Ueber das Mineralvorkommeu im Granit von Striegau, 

 insbesondere fiber den Orthorlas und dunkelgriinen Epidote."— Breslau. 



Hobbs, W. H. — " Ueber die Verwaehsung von Allanite (Orthit) und Epidote in 

 Gesteinen."— Tschermak's Min. and Pet. Mitt., 1889, i., also Johns Hopkins 

 University Circular, April, 1888. 



Lacroix, A. — " Contributions a l'etude dee Gneiss a Pyroxene et des roches a 

 Wernerite." Bull. Soc. Min., France, April, 1880. 



Tornebohm, A. E.— " Mikroskopiska Bergartstudier XIL.Epidot gneiss," Geol. 

 For. i., Stock Forh. No. 75, 1882. 



