150 THE OKYSTAL FALLS IRON-BEARIXO DISTRICT. 



schists ai'e metamorphosed volcanic rocks, and this conclusion is strength- 

 enod by detailed petrographical examination. 



PETROGRAPHICAL CHARACTERS. 



Tlie crystalline schists are fine to medium g-ralned schistose rocks 

 ■wliich var\' in color from a moderately light green for the more chloritic 

 phases to a Aery dark green and purplish-black for those in which the 

 hornblende, mica, and iron ores are prominent. The minerals of which 

 the rocks are composed, arranged in order of importance, are hornblende, 

 biotite, feldsjjar, chlorite, epidote nmacovite, quartz, magnetite, hematite, 

 ilmenite, and rutile. Under the microscope the schistose structure is seen 

 to be produced by the general parallelism of the bisilicate constituents. 

 The porphyritic texture is seen in a few specimens, and hornblende forms 

 the phenocrysts. 



Hornblende occurs in fine needles and also in coarse crystals which 

 are automorphic in the prismatic zone, but on which no terminations have 

 been observed. It also occurs rather commonly in sheaf-like bundles of 

 ragged crystals. The marked orthopinacoidal development so common for 

 actinolite is quite noticeable. The crystals show the usual strong pleoch- 

 roism: c=: bluish-green, Ijr: olive green, ix = yellow, whereb}" C>-li>>a. 

 The hornblende crystals frequently contain large quantities of the minerals 

 of the grouudmass, maiiy of them in such quantity that there are really 

 only skeleton hornblende crystals present. The general character of the 

 hornblende in all these rocks is that of a secondary porphyritic constituent, 

 and seems to be analogous to such minerals as garnet, staurolite, etc., which 

 are produced in clearly metamorphic rocks. 



Brown biotite is rather common in some of the rocks. Though usually 

 subordinate to the hornblende, it is at times the predominate bisilicate. It 

 is light brown and shows the usual characters of biotite. It is present in 

 small irregular flakes, and also in larger individuals which show poor 

 pinacoidal development. In one case such a mica individual in perfectly 

 fresh condition may be seen with its ragged edges interlocking with the 

 fringed periphery of an altering feldspar crystal. The biotite appears to 

 have derived some of its necessarj^ elements from the feldspar and to be 

 eating into it, and consecjuently to be a secondary product. 



Feldspar is not found as an original mineral in any of the crystalline 



