926 THE GEOLOGY OP MINNESOTA. 



[Pyroxenyte. Noryte. 



Remark. For some years these olivinitic and pyroxenic rocks were considered 

 a part of the Animikie, especially when they were found to be iron bearing, under 

 the name Pewabic quartzyte, while the muscovadyte, which always accompanies 

 them, and which has strong affinities with the gabbro, was assigned to the gabbro, 

 or post-Animikie. The various chapters descriptive of the geological plates were all 

 written from this point of view (vol. iv). 



It became evident, however, that this olivinitic iron ore belonged with the 

 Keewatin, and that the muscovadyte is only a regenerated basic debris of the 

 Keewatin. It remained to complete the genetic round of transformation by recog- 

 nizing the bond which attaches the gabbro to the muscovadyte, and to reach the 

 hypothesis that the gabbro itself is the last result of the metamorphism of the 

 the Keewatin greenstones. This point has since been critically examined at 

 Disappointment lake and everything seen there tends to show such a relationship. 

 The term Pewabic quartzyte is retained for this modified jaspilyte, and the term 

 Pokegama has been applied to the basal member of the Animikie. Consult the Lake 

 county chapter in volume iv. N. H. w. 



No. 505H. NORYTE (with olivine). 



A short distance north of the quarter-post between sees. 14 and 15, T. 63-9 W., south of Snowbank lake. 

 Ref. Annual Report, xvii, pages 120, 142; Annual Report, xxi, pages 151, 152. 



Meg. A rather fine-grained rock of a gray to brownish-gray color. Not gneissic. 

 Composed of grains of a glassy mineral and smaller ones, which are yellowish to 

 black in color. 



Mic. A granular aggregate of feldspar, pyroxene, olivine, magnetite and a little 

 biotite. The feldspar is largely, perhaps entirely, plagioclase. Some grains do not 

 show twinning striae, and in some the cleavage is not well marked. Such grains 

 might be quartz; however, a dozen such grains which, if quartz, would be approxi- 

 mately basal sections, were examined for interference figures and every one showed 

 a distinct biaxial figure. I think there is no quartz in the section. The pyroxene 

 is distinctly pleochroic, and is hypersthene. The minerals of this rock, except the 

 olivine, are unaltered and fresh. A little monoclinic pyroxene is also probably present, 



Age. Cabotian. 



Remark. This rock is one to which the name muscovado (or muscovadyte) has 

 been applied. u. s. G. 



