DESCRIPTION OF ILLUSTRATIONS. 149 



Fig. is. Slide 194'''''. Ilorseshoeshaped ai)iititc cut so nearly at right angles to the 

 iiiaiu axis as to remain almost black between crossed NicoJs. It ocenrs 

 in a decomposed hornblende. The rock is dioritie porphyry from tiie 

 McKibbcn Tunnel. Magnified 220 diameters. 



Fig. 19. Slide 454^^-^". Mass of ilnienite showing characteristic markings, from an 

 augite-andesite from Cedar Hill Caiion. Magnified 70 diameters. 



Fig. 20. Slide 1S2"^-"'. A peculiar secretion in a glassy augite-andesite from tlie south- 

 west rtank of Mount Kate. It is a brownish mass of pseiido-si)luM(ilitic 

 structure filled with black trichites. It much resembles a patch of brown 

 mold. Many others occur in the same slide. Magnified 45 diameters. 



Fig. 31. Slide 421'""". Symmetrically arranged acicular black inclusions found in the 

 hornblendes of diorites and andesites. The illustration is taken from a 

 longitudinal section of brown hornblende, and the direction of tiie cleav- 

 age is indicated by the arrow. Tlie rock is aporphyritic diorite from the 

 center of Cedar Hill ridge. Fig. 2G is from the same slide. Magnified 

 000 diameters. 



Fig. 22. Slide 210''-'". Secondary fiuid inclusion in feldspar. These inclusions are 

 absent from the fresh i)ortiou of the same exposure. The rock is from 

 the quarry 1,000 feet west of the Yellow Jacket east shaft. Magnified 

 800 diameters. 



Fig. 23. Slide 462"'--". The illustration shows the edge of a feldsjtar above a i)ortiou 

 of the groundmass of the slide. The fel(lsi)ar contains inclusions of brown 

 glass, which are elongated in the direction of the edge of the crystal, aiul 

 seem thus to indicate a tendency to z(mal structure in the formation of 

 the crystal. The inclusions also show a connection with tlie present face 

 of the crystal, and are continuous in a direction vertical to the face. Por- 

 tions of the viscid glass having become entangled in the feldspar during 

 its growth, the energy of crystallization seems to have been insuificient 

 to expel or cut oft" the partially inclose<l material. The rock is a glassy 

 .younger hornblende-andesite from the Geiger Grade 2,000 feet northwest 

 of the toll-house. Magnified 200 diameters. 



Fig. 24. Slide Sol-'--". Double glass inclusion in quartz. No i)art of this inclusion 

 reaches either the up[)er or the lower stirfaee of the slide, nor is tliere 

 any trace of a crack near it. The rock is from the Orerman mine, 1,142- 

 foot level. Magnified 750 diameter.s. 



PLATE IV. 



In the description of the figures on thi.s plate and the succeeding one, 

 the position of the minerals is given by their coordinates referred to- the 

 lower left-hand corner of each figure, the ordinates being written before the 



