DYKE-ROCKS RELATED TO BANAK1TE. 
131 
Fe 2 Si0 4 
= 
G • 94 
Mg 2 Si0 4 
= 
5'32 
FeO. TiO., 
= 
5-17 
FoO. Fe 2 0 3 
= 
2-09 
Ca 3 2P0 4 
= 
1-24 
In the case of this micaceous rock the “ norm ” diverges from the “ mode,” since 
much of the potash occurs in biotite and not in orthoclase. 
In the American quantitative system the rock would be classed as Shoskonose. 
Thus both chemical systems refer the rock to the same type, from which, however, it 
differs somewhat in mineral composition. As a shoshonitc it is chemically closely 
related to the banakite-like rocks described in the next section. 
Another kersantite appears to be the dark-gray dyke (625) intrusive in the gray 
granite at E 4 at a height of about 5000 feet. Under the microscope it shows long 
shreds of biotite and much-altered green hornblende (mostly uralitic after augite, of 
which a little still remains) in a ground-mass of altered prismatic plagioclastic felspars. 
Dykes Chemically Related to Banakite. 
Under this heading are here included certain dyke-rocks which bear some relation 
to the camptonites in containing basaltic hornblende as phenocrysts and also occasion- 
ally in the ground-mass, while they differ from them by the presence of numerous 
phenocrysts of felspar, some of which are of orthoclase. 
To this group belongs the brown dyke (714) in the granite at G 3 in the Northern 
Foothills. Besides the large porphyritic crystals of basaltic hornblende referred to on 
p. 35 it shows also numerous phenocrysts of felspar and a few of augite. The felspar- 
phenocrysts are mainly of labradorite, with symmetrical extinctions in albite-lamellse 
of 26°. Others, however, with low refraction and showing no twin-striations are of 
orthoclase, while some with mottled extinctions and refraction about the same as that 
of Canada balsam are probably of anorthoclase. A few rounded phenocrysts of analcite 
are also present (see Plate IX, Fig. G). 
The ground-mass consists of a holocrystalline medium-grained aggregate of 
plagioclastic felspars (mainly in rectangular sections, but also in laths), prismatic 
crystals of pale-purple augite, and magnetite. Borne of the rectangular felspars in the 
ground-mass are of labradorite giving symmetrical extinctions as high as 25°. 
Apatite-needles are plentiful, and shreds of brown altered hornblendie material are 
scattered through the slide. 
A coarse-grained inclusion consists of an aggregate of felspar with refraction near 
that of Canada balsam, pale-green to purple augite, basaltic hornblende, and analcite, 
with large needles of apatite and much magnetite. 
A somewhat similar dyke-rock (720) comes from Cathedral Rocks at E 2 . It shows 
porphyritic crystals of labradorite (symmetrical extinctions of about 28°) and green 
uralitic pseudomorphs, in a ground-mass of rectangular felspars and long needles of 
s 2 
