PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 621 



Noryte. Gabbro.] 



The iron ore is undoubtedly magnetite; it is in small grains with more or less 

 distinct faces, but with the angles rounded. 



The pyroxene and iron ore are probably older than the mass of the rock, 

 which is composed of quartz and feldspar, and the biotite encloses all. 



The feldspar is abundant; it frequently shows polysynthetic twinning, and is 

 thus plagioclase; but the kind of plagioclase is uncertain. There is also considerable 

 feldspar which is not twinned and which may be orthoclase, or untwinned plagioclase. 



The quartz is in fine grains, even finer than most of the feldspar. There are 

 many grains, which show no cleavage, or twinning, whose nature it is not easy to 

 determine. Many of such grains, supposed to be quartz, give a biaxial interference 

 figure; and others give no distinct figure. I examined about twenty sections which 

 I thought might be basal sections of quartz; only one out of these twenty gave a 

 distinct uniaxial interference, figure; this was tested and found to be +. Four or 

 five gave biaxial figures, and the others gave no definite figures. The feldspar is 

 unaltered, and so is hard to distinguish from quartz, when twinning, cleavage or 

 interference figures are not to be seen. It is my opinion that there is much less 

 quartz in the rock than I had supposed. Thus, so far, I am sure of but one grain; 

 there are, however, undoubtedly more, but I should guess that quartz makes up less 

 than one-tenth of the rock, and I feel certain that it does not make up one-fifth of 

 the rock. 



The magnetite of Nos. 982 and 983, was tested for titanium, but none was found. 



Age. Probably Keewatin metamorphosed by Cabotian gabbro. 



Remarks. This rock is one of those to which the term " muscovado " has been 

 applied. This specimen now shows nothing that can be taken as proof of an original 

 clastic nature. It is lithologically a fine-grained quartz biotite noryte. It may be 

 a recrystallized sediment or an original eruptive; but from its field relations and 

 from general considerations, it is thought probably not to be in its present condition 

 a true eruptive. It seems to represent a Keewatin rock modified by the gabbro, 

 although originally it may have been of igneous origin. Compare rocks Nos. 1089- 

 1092. u. s. G. 



No. 984. GABBRO (?) 



Same place as No. 982. 



Eef. Annual Report/ xv, pages 351, 392. 



Meg. A fine-grained, gray, granular rock with biotite. 



Mic. This rock is in general similar to Nos. 982 and 983. The section shows 

 apparently quartz, feldspar (usually kaolinized), biotite, hornblende, pyroxene and 

 magnetite. 



One section. 



Age. Probably Keewatin metamorphosed by Cabotian gabbro. u. s. G. 



