PLATE VII. 
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Photomicrographs of Phonolite. 
A, Pkonolite (456 C- C.) from northern slope of Big Bull Mountain. Composed of soda-orthoclase, nephe- 
line, nosean, sodalite, analcite, and segirine. Characteristic texture due to abundance of nepheline. 
Veinlet crossing the plate is filled with analcite. .Egirine in small needles is particularly abundant 
near the veinlet. Magnified 28 diameters. 
B, Phonolite (209 C. C.) from summit of hill northeast of Cameron. Ragged individuals of aegirine inclosing 
prisms of nepheline and surrounding cores of segirine-augite. Magnified 28 diameters. 
C, Phonolite (455 C. C.) from hill east of Bull Cliff. Trachytic flow texture of groundmass and phenocrysts 
of soda-orthoclase and a?girine-augite. In the upper left-hand corner of the plate are crystals of 
nepheline inclosed by analcite. Magnified 28 diameters. 
D, Phonolite (251 C. C.), 2,000 feet N. 30° E. of Copper Mountain. Nepheline (A r ) somewhat turbid through 
decomposition, and aegirine (£) inclosed in a large individual of primary analcite (M). Holes in 
the section are indicated by II. Magnified 28 diameters. 
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