in Norway and in Canada, 3 



stituents. In this way, there is caused a characteristic streaked 

 appearance, sometimes with broad black or dark grey bands, and 

 sometimes with the same streaks, narrower an] farther from each 

 other, according as the mica is more plentifully or more sparingly 

 distributed in the rock. The grains of feldspar, quartz and mica, 

 are mostly rather small in this variety of gneiss, so that it seldom 

 becomes coarsely granular." Gcea Norvegica^ p. 251. Through 

 a gradual disappearance of the feldspar ; the gneiss sometimes 

 changes into mica schist, and through a gradual change in 

 the position of the laminae of mica, from that of parallel layers, 

 to being irregularly distributed, the gneiss often passes into 

 granite. Of the many varieties of gneiss, one deserves special 

 notice ; it has been called Porphyroid gneiss, and differs from 

 the characteristic gneiss in containing lenticular-shaped aggrega- 

 tions of feldspar in a fine schistose matrix. It is this variety 

 which has sometimes been called Eye gneiss. 



2. Hornblende gneiss, differing from the characteristic gneiss in 

 having exchanged the scales of mica for crystals of hornblende, 

 arranged parallel with each other according to their longest axis- 

 Sometimes however, the hornblende has only partially supplanted 

 the mica, in which case intermediate varieties are formed between 

 the hornblendic and common gneiss. Through gradual disap- 

 pearance of both quartz and feldspar, the hornblende gneiss often 

 changes into hornblende schist, and sometimes through a change 

 in the structure of the rocks from schistose to granular, syenitic 

 and greenstone rocks are formed. 



3. Granite of the usual composition. It often occurs as a very 

 coarse grained aggregation of dark red orthoclase with sparingly 

 distributed quartz and mica. 



4. Mica schist, composed of quartz and mica, with a schistose 

 structure, and often containing garnets. It exhibits transitions 

 into hornblendic schist as well as into gneiss, (fee. 



5. Hornblendic schist, forming transitions into greenstone, and 

 when the structure continues coarse grained, into diorite and 

 diabase. 



6. Chlorite schist, consisting principally of chlorite and a little 

 feldspar ; here and there interwoven with fibres of hornblende. 



7. Talc schist, mostly quartzose. 



8. Quartz, as granular quartz rock, forming layers and zones ; 

 sometimes slaty, forming quartz slate. 



9. Euphotide, consisting of brown diallage and white feldspar. 



