DETAILED DESCEIPTION OF SLIDES. 133 



adhesive glass during crystallization. Some of these inclusions are shown 

 in Fig. 23, Plate III. Zonal structure is beautifully developed in many of 

 these feldspars. 



The hornblendes are of a somewhat dull yellowish-green color and 

 very solid. They are especially remarkable from the fact that scarcely 

 any of them show even a trace of a black border. There is a large quan- 

 tity of augite of exceptionally pale color. It is faintly dichroitic and 

 crystallized in unusually long needles. The sections and angles of extinc- 

 tion leave no doubt as to its nature. There is a single excellent biotite in 

 the slide. Many colorless apatites and a considerable quantity of magnetite 

 are present. The base shows a felt-like structure which appears to be due 

 to the presence of minute opaque microlites. 



Slide 470. Mouut Abbie. 



Gray coarse-grained variety. — This ii} a coarse gray porous rock, strongly re- 

 sembling a hornblende-trachyte in appearance. Under the microscope, 

 however, it is plain that nearly or quite all the feldspars ai-e triclinic, and 

 they give labradorite angles of extinction. Many of the smaller labrador- 

 ites are simple individuals. The hornblende and augite are such as are 

 common in the hornblende-andesites, but the hornblendes show only very 

 narrow black borders. There are about twice as many hornblendes as 

 augites. The groundmass is microlitic, and no base is visible. 



Slide 467. 1,000 feet north-uorthwest of Flowery Peak. 



Porphyry with dark groundmass. — This is n coarse-graincd rock in which large 

 crystals of feldspar are separated out in a dai'k, rather compact groundmass. 

 Mica as well as feldspar is visible. Most of the feldspar crystals show twin 

 striations, but there are some Carlsbad twins and simple crystals, none of 

 which, however, are probably orthoclastic. Many of the larger crystals, 

 which are well developed, show zonal structure. The maximum angles of 

 extinction correspond to labradorite. The feldspathic microlites are shorter 

 and broader than is usual, and a few are possibly sanidin, but the great 

 majority are certainly triclinic. I noticed no inclusions in the feldspars 

 beyond apatite. Hornblende and mica are almost wholly represented b}' 



