Aift. IX.3 Herrick-Johnson, Geology of the Albuquerque Sheet, 225 
color is black to dark brown with small phenocrysts of plagio- 
clase and grains of olivine. In the section the largest elements 
are polysomatic grains of the plagioclase with conspicuous 
albite twins. The mineral is fresh and in definite crystal form. 
The extinction angle at right angle to the albite twinning plane 
is near 35° and indicates a composition like anorthite but the 
optical behavior is negative and the high colors of polarization 
suggest laboradorite. Smaller lath-shaped crystals of plagioclase 
fill the deep colored magma. Next to the first order plagioclase, 
the most conspicuous elements in the section are the brilliantly 
polarizing grains of olivine some of which preserve their crys- 
talline form. The olivine is remarkably fresh and contains few 
inclusions. The augite which is of the basaltic type plays a 
very insignificant role being restricted to grains scattered in the 
interstices of the small plagioclase crystals. The magma is 
granular and opaque and contains much magnetite and brown 
suffusions. Amygdules of isotropous and amorphous materials 
occur sparingly. 
In order to show the extremes of structure the following 
descriptions are appended derived from basalts found along the 
Rio Grande east of the Cochiti range selected to show the latest 
and earliest of several flows at that place. It will be seen that 
there is evidence of some alteration in the lower member. The 
intervals are irregularly filled with volcanic and scoriaceous 
material. 
No. 495. Lowest Member of a Series of Basaltic Flows 
in White Canon, south-west of Santa Fe. A somewhat vesicu- 
lar massive basalt with numerous spots of reddish decomposi- 
tion, imparting a rusty color to the entire rock, strongly con- 
trasting with the fresh and glossy black appearance of the upper 
flows of the same series. In many places large zeolitic inclu- 
sions occur, having a radiated structure and a whitish or green- 
ish color, which determines it, apparently, as analcite. The less 
altered portions show the feldspathic elements to be unaltered. 
The whole crystalline body of the rock is made up chiefly of 
plagioclase of two distinct orders. Those of the first order are 
large, well-formed crystals, exceeding those of the magma many 
