1893.] NEW YOllK ACADEMY OF SCIENCES. 209 



making au angle of 5°, with the axis of greatest elasticity in the 

 quartz. 



In nearly all sections the hair-like bodies are more or less 

 bent, broken and stretched apart. Sometimes it is evident that 

 this results from a crack through the quartz, but more often it 

 is impossible to detect any sign of such fracture. Apparently 

 the quartz has been sufficiently plastic to yield to strains whicla 

 broke the rutile. 



Inclusions of zircon and other small crystals or fragments in 

 the quartz sometimes show several short cracks radiating from 

 them. A similar occurrence is also seen in the feldspar. In 

 the case of cracks radiating from hornblende in a porphyritic 

 rock Becker* has suggested that they might result from the 

 forcible expansion of the hornblende in process of growth. But 

 in the present instance it seems more probable that they result 

 from the unequal resistance offered by the included mineral and 

 the quartz or feldspar to the pressure to which the rocks have 

 been subjected. Other effects of pressure are seen in the marked 

 undulatory extinction alwaj's present, in the more or less shat- 

 tering of the quartz, and in the development in it of abundant 

 secondary fluid inclusions. 



There is wide variation in the character of the feldspar. In 

 the normal granitite orthoclase is most abundant, in the granu- 

 litic variety microcline is often conspicuous, while in the more 

 basic granitite and diorite a basic plagioclase replaces the more 

 acid species. 



Microperthite is common, though rather less so than in the 

 gneiss. Feldspar is also sometimes intergrown with quartz, 

 forming micropegmatite. As is usually the casef, this micropeg- 

 matite fills small spaces between the larger rock constituents, 

 and is evidently of late formation. In many instances it is 

 clearly secondary, having formed in cracks made by disturbances 

 subsequent to the solidification of the rock. So often is this 

 true that it is highly probable that all of the micropegmatite is 

 of secondar}' origin. Enough instances of each secondary 

 formation of micropegmatite have been described^ to indicate 

 that it is a general, rather than exceptional, phenomenon. 



* Becker, G. F., " Quicksilver deposits of the Pacific Slope," p. 100. 

 t Rosenbusch, Mic. Phys. Mass. Gest., p. ;»• 



t Irving, R. D., "The Copper Bearing Rocks of Lake Superior.'' Monograph 

 v., U. S. G. S., p. lU. 



Judd, J. W., Quart. Jour. Geol. Soc. XLV., p. 175-18G. Ibid. XLIL. p. 7-2. 



Romberg, J., Neues Jahrbuch, fuer Miueralogie, etc-, B. B. VIII. p. :il4-:m: 

 374-378. 



Hobbs, W. H., Bull. Geol. Soc. America. IV.. p. 171. 



Trausactioiis N. Y. Acad. Sci. Vol. XII. July G, 1893. 



