PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 819 



Granite. Diabase.] 



which is prevalent, spreads irregularly over their surfaces, as exposed by the section, 

 but still it is frequently mostly confined to the central parts, and occasionally a 

 grain shows a distinct bordering secondary growth. The abundant quartz has a 

 shadowy extinction and forms the cement for the feldspars. One section. 



Age. Archean. N. H. w. 



No. 1999. GRANITE. 



Same place as No. 1993. 



Ref. Annual Report, xxiv, page 5. 



Meg. Granitic boss underlying No. 1998, its structure rudely conformable with 

 it, having inclusions of schist and gneiss. 



Mic. ThQ feldspars are mostly distinctly interlocked with each other, but the 

 ijitartz, which is of later origin, fills the angles and often isolated spaces within the 

 feldspars. The weathering effect is spread uniformly through the feldspars. Epidote, 

 s/i/iene and hornblende are in small amounts. One section. 



Age. Archean. 



llcntnrk. Some discussion of the structural relations of the granites and schists 

 at this point, on Vermilion lake, may be found on pages 2-11 of the Twenty-fourth 

 Annual Report, based on the facts of field observation. N. H. w. 



No. 2001. DIABASE. 



From a dike, sec. 14, T. 63-18, two and a half feet wide, cutting the face of the bluff and running E. N. E., 

 Vermilion lake. 



Ref. Annual Report, xxiv, page 8. 



Meg. Fine grained near the centre of the dike. 



Mic. The augite has so small an optic angle that the interference figure in 

 convergent light has an action and appearance resembling that of a uniaxial mineral, 

 thus allying this diabase with some of thegabbrosof the Keweenawan (Nos. 291, 297). 

 It gives the positive sign with the mica plate, n s being in the acute optic angle, but 

 its elongation is negative, /. e., n v forms a smaller angle with the vertical crystallo- 

 graphic axis than n e , a fact which shows that it is allied to cegyrhie* This augite is 

 rarely ophitic with respect to the feldspars of the second generation, the first feldspars 

 having evidently also preceded, but being so few as to not come into contact with 

 the augite. Magnetite in scattered grains, npliene in a few irregular grains, calcite 

 and i>rniiiin{ ?) filling large idiomorphic crystal spaces which may have been once 

 occupied by olivine, are the only other ingredients. One section. 



Age. Keweeuawan(?) 



Hi-mark. The slide presents the appearance of a rock whose individual crystals, 

 probably once in ophitic relation, have been broken up into many angular individ- 

 uals with varying orientation, this being due apparently to the exigencies of flowage 



* Jfiniralogie cle France, vol. 1, p. 568. 



