!l8 



C. H. GORDON 



or stringers one-half to one inch in width, one {a) consisting of basic 



(probably hornblendic), and the other (&) of feldspathic material. 



In places masses of the pyroxenite appear as inclusions in the syenite 



dikes, and without close examination 

 might easily be taken for a segrega- 

 tion of basic material in the syenite. 

 Under the microscope the pyrox- 

 enite is shown to consist chiefly of a 

 pale, almost colorless monoclinic 

 pyroxene, apparently augite. It is 

 for the most part coarsely crystal- 

 lized and has a pronounced pris- 

 matic cleavage. Polysynthetic twin- 

 ning in thin lamellae parallel to the 

 orthopinacoid (loo) is frec{uent, 

 giving a pronounced diallage-like 



appearance, probably due to the development of gliding planes as 



a pressure phenomenon.^ 



I i'l "P^/ to >revii^e~" 



IfS^Qucurrzite.E" 



Fig. 2. — Showing pyroxenite in 

 tercalated in the quartzite. 



ilMiiliiiPijroxeni\e 

 Quart x'ltt, 



Fig. 3. — Showing the pyro.xenite interbedded with the quartzite and including 

 portions of the latter. 



Further evidence of dynamic movement appears in the slight lack 

 of correspondence in the continuation of cleavage cracks, in the bend- 

 ing and fracturing of lamellae, and especially in the extinction shad- 



I F. ZiRKEL, Lehrbuch der Petrographie, Vol. I, p. 612. 



