466 THE CEYSTAL FALLS lEON BEARING DISTEIGT, 



is in small dark greenisli-brown flakes interspersed between quartz and 

 feldspar grains, wliicli together constitute a matrix surrounding the other 

 components. The quartz is unusually free from inclusions. It contains a 

 few liquid inclosures and occasionally a few flakes of biotite and needles of 

 hornblende. The plagioclase, where present, is in irregular grains Avith 

 ragged outlines, as though a newly formed mineral. It appears to act the 

 part of a cement surrounding the other minerals with which it is in contact. 

 Small round grains of sphene and magnetite occur very abundantly scat- 

 tered through the matrix. Often the magnetites are surrounded by borders 

 of sphene ; hence it is probable that this mineral is a titaniferous variety and 

 that the round grains of sphene are pseudomorphs after magnetite grains 

 that have been completely altered. 



In a few specimens large colorless areas with the outlines of porphy- 

 ritic crystals are observed in the midst of the finer-grained groundmass of 

 schist. Between crossed nicols these break up into a coarse-grained aggre- 

 g-ate composed of the same minerals that constitute the rest of the rock, 

 except that in it altered plagioclase is common and amphibole is rare. 

 These probably represent phenocrysts of plagioclase which have suffered 

 alteration into quartz and new plagioclase that may differ somewhat from 

 the feldspar of the original crystal. 



The banding of some of the hornblende-schists has already been 

 referred to. Under the microscope the only difi'ereuces noted in the bands 

 are the quantity of hornblende present in them and a variation in the 

 coarseness of grain. The coarsest of the bands have the composition and 

 structure of the schistose greenstones. They contain large quantities of 

 plagioclase, both fresh and altered, and large grains of hornblende that are 

 not in the definite prismatic form characteristic of this mineral in the main 

 mass of the rocks. 



OEIGIN OF THE AMPHIBOLE-SCHISTS. 



From the gradations often observed between the hornblende-schists 

 and the greenstone-schists, it is plain that the two rocks are g'enetically 

 related. The latter, from their similarity to schistose dike greenstones in 

 ■composition and structure, are believed to have been derived fi'om massive 

 diabases or gabbros. The hornblende-schists are in all probability derived 

 ^from similar basic rocks, though the presence in them of what appears to 



