ELY GREENSTONE. 153 



SCHISTOSE GREENSTONES. 



The various greenstones thus far described liave been very much 

 changed by chemical action, as is shown by the number of secondary 

 minerals which now replace the original ones. In many cases dynamic 

 action subsequent to or accompanied by the above changes has produced 

 schistose forms of these greenstones. These schistose greenstones are not 

 nearly so common, however, in the Vermilion district as one would be led 

 to suppose from a perusal of the literature which has been published on this 

 district. In this literature tliese rocks have frequently been spoken of as 

 greenstone-schists. This term seems to the writer to convey a wrong idea 

 of the character of the rocks as a whole, though it is fitting in certain cases. 

 The greenstone-schists or green schists are in reality a very subordinate 

 phase of the El}'' greenstone, and in the great majority of cases are of purely 

 local occurrence and very subordinate extent. They have been formed 

 along zones of excessive deformation and grade into massive granular rocks. 

 For this reason the term schistose greenstone has been preferred to indicate 

 them. In these schistose rocks all of the original minerals have been 

 changed by metasomatic action, and as a result of movement in the rocks 

 produced by shearing stresses, the original textures have also been almost 

 completely obliterated. 



GENERAL CHARACTERS. 



These rocks are scliistose in character and appear in various shades of 

 green. Only one macroscopic structure has been observed which would 

 lead to the determination of the original characters of the rocks. An imper- 

 fect, nearly obliterated, amygdaloidal structure was observed in one case. 

 A microscopic study of the rocks shows that the constituents are small and 

 the rocks very dense in texture. The various minerals to be enumerated 

 generally have their long directions approximately parallel, this aiTangement 

 producing a schistose structure. In some cases almost complete recrystal- 

 lization seems to have taken place, and in these cases larger individuals have 

 been produced. Occasionally the hornblende and chlorite appear in large 

 porphyritic individuals inclosing other constituents of the rock. Constituents 

 of these rocks are biotite, muscovite, chlorite, sericite, calcite, epidote, 

 zoisite, pyrite, and limonite. In some cases the secondarily produced 

 hornblende has undergone a tertiary change and has been chloritized. 



