PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 903 



Graywacke.] 



Meg. A rather coarse-grained, pinkish-gray granite composed essentially of 

 quartz, feldspar and hornblende. Epidote is present, and sometimes small crystals 

 of sphene. This rock is a typical specimen of the Saganaga granite. 



Mic. The section shows a granite composed mainly of quartz and feldspar. 

 The latter is commonly clouded and in part altered to fine flakes of a micaceous 

 mineral. The feldspars appear to be in part orthoclase and in part plagioclase near 

 oligoclase. Hornblende is present and has largely altered to a mixture of chlorite 

 and epidote. Sphene is present in small amount, as are also calcite, magnetite and 

 apatite. Two sections. 



Chemical analysis. An analysis of this rock by Mr. A. D. Meeds gave the following result: 

 SiO 2 A1,O 3 Fe 2 O 3 and PeO CaO MgO K 2 O Na 2 O H 2 O Total 



69.34 17.25 2.46 3.43 1.18 .71 4.33 1.17 99.87 



Age. Archean. u. s. G. 



No. 739G. GRAYWACKE. (Matrix of altered conglomerate. ) 



S. W. J4 S. E. }4 sec. 1, T. 64-7, south of Kekequabic lake. 



Ref. Annual Report, xxi, page 59 ; Annual Report, xxiv, page 88. 



Meg. Gray, fine, firm. 



Mic. The rock contains quite a number of angular clastic quartzes, also areas, 

 sub-rounded or angular, of a mosaic of quartfe grains that closely interlock in the 

 manner of the quartzes of jaspilyte; in these the size of the quartz grains, while 

 about uniform in any individual area, varies from fine to coarse. Other areas seem 

 to have been occupied by different rock pebbles, amongst which some were apparently 

 fine diabase or basaltic (glassy) rock which now is thickly sprinkled with adinolite, 

 or with fine scales of yellowish -green biotite, but these can with difficulty be distin- 

 guished from the general matrix. Magnetite and sphene (the latter scantily) are 

 scattered through the slide. Feldspars in conspicuous grains are as abundant 

 as the quartzes. They are much altered and are sometimes pierced by actinolite 

 and biotite. They show no marginal enlargements. Their edges are ragged and 

 the fine matrix fills in the angles between the ragged projections, and also enters 

 fissures. 



The rock is simply a densely compacted, fine debris, the alteration of whose 

 individual grains was accomplished mainly prior to their incorporation in this rock. 

 It is probable that the actinolite is of secondary origin. It is impossible to say 

 whether quartz has been transformed. The only indication of such change that is 

 apparent is the fact that sometimes the actinolites penetrate it for short distances, 

 and that different quartzes are sometimes interlocked in a secondary manner. One 

 section. 







Age. Archean (Upper Keewatin). N. H. vv. 



