BANAKITE. 349 



side of the amphitheater at the head of Stinkingwater River (1460), and 

 from a dike on the Ishawooa (1702) 



The rock of the third analysis (1699) is similar to the last, but is 

 more feldspathic. It forms a dike in the Ishawooa Canyon. It is dark 

 gray and waxy looking, with tabular phenocrysts of feldspar, and many 

 smaller ones. In thin section it is holocrystalline, with abundant lath-shaped 

 twins of orthoclase, having a rectangular central inclusion of labradorite 

 (An 3 Ab 2 ). There is an isotropic cement between the feldspars, which in 

 places is cloudy, and may be analcite or sodalite. Biotite and augite are 

 abundant in small crystals, besides magnetite and a little serpentine, which 

 appears to have been derived from small olivines. The phenocrysts are 

 labradorite (An 2 Ab 3 ), some of which have borders of orthoclase. There is 

 also a large individual of isotropic mineral without crystallographic bound- 

 ary. This rock is shown in PI. XXXVIII, fig. 2. 



A closely related rock (1466) from a dike near the head of Stinking- 

 water River has almost the same chemical composition (analysis 4). It 

 carries more phenocrysts of serpentinized olivine. In thin section it is 

 coarser grained than the last variety, and the feldspars are more altered 

 and less distinct. The mineral composition is like that of the rock just 

 described, but a few of the augites are bright green, indicating an approach 

 to segirite-augite. 



Analyses ba and 5b of the table on page 347 are of a leucite-bearing 

 variety (1643), previously alluded to as forming a massive surficial sheet 

 of lava immediately overlying the shoshonite which occurs on the south- 

 east fork of Beaverdam Creek, and whose chemical composition is given in 

 analysis 2 of the table on page 340. Its chemical composition is but 

 slightly different from that of the rock last described (1466), analysis 4. 

 The rock is dark gray, with a somewhat waxy luster, and carries small 

 phenocrysts of feldspar, serpentinized olivine, and a few augites. In thin 

 section it is holocrystalline, and has a groundmass of microscopic leucites 

 and unstriated feldspars, which appear to be orthoclase, but may be plagio- 

 clase with low angles of extinction, besides augite and magnetite and some 

 serpentine. There are a few patches of light-brown mica. The pheno- 

 crysts are labradorite, serpentinized olivine, and fewer augites, magnetites, 

 and stout apatites. The crystals of leucite have the characteristic form and 

 inclusions, and in places are somewhat altered. 



