242 ANNALS NEW YORK ACADEMY OF SCfENCES 



Analysis of Augen Gneiss Norm 



Per cent Per cent 



SiOz 67.02 Quartz 19.08 



AI2O3 13.96 Orthoclaso 31 .69 



Fe203 2.36 Albite 30.39 



FeO 2.73 Anorthite 6.12 



MgO 1.27 Diopside 5.74 



CaO 2.69 Hypersthene 1.26 



Na^O 3.61 Magnetite 3.48 



K2O 5.27 Tlmenite 2.62 



H2O+ 36 



H2O — 02 Total 100.38 



TiO, 1.41 



Total 100.70 



Magmatic symbol II. 4.23. Adamellose. 



The analysis would rather seem to uphold the above conclusions as it 

 corresponds to that of an igneous rock of about the composition of a 

 quartz monzonite. 



There are other features, however, which cannot very well be explained 

 by such a hypothesis. The occurrence of the "augen" gneiss in bands of 

 varying width and their gradation into mica schist or hornblende schist 

 cannot very well be explained by such a supposition. The fact that where 

 the "augen" gneiss is associated with mica schist, its matrix has the com- 

 position of the mica schist and where, with hornblende schist, that of the 

 hornblende schist, does not favor such a conclusion. If the "augen" 

 gneiss represents a metamorphosed igneous rock in which the feldspar 

 "augen" represent original unsheared feldspar crystals, the original rock 

 must have had a very coarse granitoid texture or else a porphyritic texture 

 in which the phenocrysts were feldspar.. In either case, it is hard to see 

 why these "augen" of feldspar should have their present distribution in 

 local belts through the rest of the rock. It is also hard to account for 

 such a variation in matrix as is represented in different places. 



The apparent gradation of a pegmatite sheet into "augen" gneiss by 

 a thorough injection of the adjoining schist with pegmatitic material, 

 and the final gradation of this into true schist with only a few "augen" 

 of feldspar, suggests that the "augen" gneiss represents sheared zones of 

 schist which have been thoroughly injected and permeated with pegma- 

 titic material consisting largely of potash feldspar together with some 

 plagioclase and quartz. The only peculiar feature, assuming that this 

 is the correct explanation, is that the feldspar took on a more or less 

 crystalline outline. That this injection belonged to the earlier stages 



