ELY GREENSTONE. 157 



possessing on the whole a massive structure, nevertheless have, as it were, an 

 incipient fissility, or cleavage, which has been produced by the process of 

 recrystallization through which they have gone, as the result of which there 

 has been a production of amphibole needles and chlorite flakes, and also a 

 general tendency toward a parallel arrangement of the needles and flakes. 

 The secondary feldspar has also been affected in its ciystallization, and 

 aids in emphasizing the parallel structure. This parallelism has developed 

 a fissility which is not sufficiently marked to warrant their designation as 

 schists. They merely split more readily in one direction than in another. 



When the contact between the main granite masses and the Archean 

 greenstone is approached, the Archean rocks are usually found to have lost 

 all of their characteristic features and to have been recrystallized into 

 amphibolitic schists and gneisses which very rarely retain any recognizable 

 greenstone character. The gradation is, however, so gradual and the steps 

 can be followed so clearly in the field that after a field inspection no doubt 

 as to the correctness of the above conclusions can remain in the mind of 

 any close and impartial observer. 



MINERALOGIC COMPOSITION OF THE METAMORPHOSED ROCKS. 



Thes6 amphibole-schists and mica-schists, derived from the green- 

 stones, consist of the following constituents in varying proportions: Com- 

 mon green hornblende, actinolite, biotite, muscovite, chlorite, epidote, 

 calcite, sphene, quartz, feldspar, pyrite, and magnetite. The mica is pres- 

 ent in very small quantity and is always associated with amphibole. It is 

 only occasionally that the mica occurs in such quantity that the rock can 

 be referred to as a mica schist. Banding is very commonly present, 

 as the concentration of some of the darker minerals was greater in certain 

 portions than in the areas immediately adjacent. 



The origin of these metamorphosed greenstones, now schistose amphi- 

 bolitic rocks, is such as would be expected from their distribution and from 

 their relationship to the granites. They always lie between the normal 

 greenstones and the granites, occupying a belt of varjang width, which 

 it is impossible in the field to delimit sharply. This zone of schists has 

 therefore been only approximately indicated on the maps. 



The presence of these amphibolitic schists adjacent to the granite has 

 been noticed by nearly every observer who has been in this district. On 



