940 THE JOURNAL OF GEOLOGY. 
crystalline, except for occasional possible remnants of glass base. 
There are also small irregularly shaped crystals of augite and 
olivine, besides magnetite and much apatite in long, slender 
needles. Orthoclase and leucite are not uniformly mingled, but 
are clustered in groups. The orthoclase crystals are rectangular 
prisms, twinned according to the Carlsbad law. Very rarely they 
‘contain minute cores of lime-soda-feldspar, with symmetrical 
extinction angles of 30°, corresponding to labradorite. The 
leucites are partly idiomorphic, partly allotriomorphic. In places 
they are decomposed to a zeolitic mineral. The other constitu- 
ents of the rock are very fresh. Owing to the small amount 
of material collected no separations or partial analyses were 
attempted. 
The rock, whose chemical composition is given by analysis 2, 
occurs as a four-foot dike on the divide between Lamar River and 
Crandall Creek. It is dark colored and aphanitic, with abundant 
phenocrysts of augite, 5 to 1o™™ in diameter, and smaller ones 
of olivine. On the sides of the dike the rock is glassy and black. 
The body of the dike is holocrystalline and very fine grained 
when seen in thin section. The groundmass consists of indis- 
tinctly outlined, lath-shaped feldspars with low extinction angles, 
there is also an indistinct feldspathic mineral as cement, which is 
clouded. The lath-shaped feldspars appear to be in part, at least, 
orthoclase with minute prismatic cores of lime-soda-feldspars. 
Nothing resembling leucite is present. The feldspathic matrix 
is crowded with microscopic crystals of augite, magnetite and 
brown biotite in thin tablets. The groundmass of the glassy 
margin of the dike is brown glass with microlites of augite and 
some of lime-soda-feldspar. The augite phenocrysts are light 
green in thin section and are filled with irregularly shaped inclu- 
sions of crystalline groundmass containing rods of ilmenite. 
There are also inclusions of small olivines and magnetite. The 
olivine phenocrysts are idiomorphic and quite fresh, with small 
inclusions of magnetite and glass, and occasionally bays of 
groundmass. 
The glassy groundmass of the margin of the dike is unlike 
