148 The American Geologist. September, looi. 
have a linear arrangemcMit, thus t^iviiif^ the rock a well marked 
banded appearance. 
A characteristic feature of the norytes is the development of 
secondary hornblende along certain planes. This shows itself 
in narrow green bands or lines traversing the rock in various 
directions and standing out on weathered surfaces. When a 
number of these are present they give the rock a greenish 
color. 
Almost without exception the norytes are remarkably fresh 
and unaltered. They are readily seen with the unaided eye to 
be composed of a clear, glassy feldspar and a reddish-brown or 
dark hypersthene which may or may not possess a bronzy lustre. 
In addition to these essential constituents the rock is shown by 
the microscope to contain a little accessory diallage, together 
with magnetite, apatite and secondary hornblende. The mag- 
netite is by no means abundant and is. often absent from the 
sections. 
The feldspathic constituent is byfozvnitc which was found 
to be slightly more basic than that of the diorytes. It gave ex- 
tinction angles as high as — 22° on oP (001) and — 31° on x P ^ 
(010). The specific gravity as determined by the Thoulet so- 
lution was 2.74. This mineral seldom exhibits crystal outlines 
but occurs in rounded or irregular grains. As in the diorytes 
the feldspar is' commonly finely striated, though in some cases 
these twinning lamellae are wanting. Abundant inclusions, like 
those so characteristic of the plagioclase of the gabbros, are 
usually found. 
The pyroxene is represented almost wholly by the ortho- 
rhombic variety, hypersthene. This occurs in grains that are 
more or less rounded and often elongated in the direction of 
the vertical (c) axis. The most striking characteristic of this con- 
stituent is its marked and often brilliant trichroism. The ray 
vibrating parallel to the brachydiagonal axis ( ft ray) is reddish 
brown; that parallel to the macrodiagonal axis (b ray) is light 
greenish yellow ; while the one vibrating parallel to the vertical 
axis ( c ray) is green. There is a well developed cleavage par- 
allel to the unit prism, and in addition distinct partings parallel 
to the macropinacoid and brachypinacoid. These show them- 
selves in basal sections as two sets of cracks at right angles to 
each other and forming angles of 45° with the cleavage lines. 
