ELY GREENSTONE. 151 



rocks are very mucli altered. The original minerals that remain are 

 very few. The microscope discloses the following original constituents: 

 Hornblende, augite, feldspar, quartz, titaniferous magnetite, and apatite. 

 The oi'iginal hornblende is the common brown vai'iety. The augite varies 

 from yellow to yellowish green and possesses its normal characters. The 

 feldspar usually shows bi'oad twinning lamellae, although in some cases 

 it was found in imperfect sheaves. In one case it Avas distinctly seen 

 to have been formed pi'ior to the titaniferous magnetite, as the magnetite, 

 occurring in large plates, incloses lath-shaped feldspars. The feldspar is 

 generally very much decomposed, so much so that one can not determine 

 its exact characters. It is prtsumed to be a labradorite. There is very 

 little quartz, but some was found occurring in micro23egmatitic intergrowth 

 with the feldspar, and is presumed to be a primary constituent. Sometimes 

 it fills irregular interstices between the other minerals as primary quartz 

 representing the last product of the crystallization of the rock. Magnetite 

 and apatite show nothing uncommon. 



The secondary constituents are common green hornblende, actinolite, 

 biotite, chlorite, sericite, epidote, zoisite, sphene, rutile, feldspar, quartz, 

 pyrite, and hematite. The feldspar has usually altered to a mass of sericite, 

 kaolin (I), feldspar, and quartz. In some cases it is completely saussuritized. 

 There were observed occasional irregular but in general rounded serpen- 

 tinous areas, which are strong'ly suggestive of aggregates of olivine indi- 

 viduals in which the olivine possesses no definite crystallographic outline. 



The great majorit}^ of the greenstones are massive rocks, varying from 

 fine to coarse in grain. The textures they originally possessed have to a 

 certain extent been obscured by the various processes of alteration to which 

 they have been subjected. Both fine- and coarse-grained greenstones and 

 all of the intermediate phases show locally porphyritic texture, the pheno- 

 crysts being usually of feldspar, but occasionally of brown hornblende. 

 In the coarse-grained rocks the ophitic texture pi'edominates ; in the 

 even-textured, fine-grained rocks the following are commonly developed: 

 Ophitic, microophitic, intersertal, pilotaxitic, hyalopilitic, flowage, and 

 spherulitic textures. The ophitic and microophitic textures are the most 

 common, and the mineralogic composition is generally that so characteristic 



