424 WEED AND PIRSSON 
times the Carlsbad. The determination of this feldspar as albite 
is based upon the facts that in sections in the zone perpendicular 
to 6 (O10) chosen according to Michel Lévy’s method, the 
maximum extinction angle is 16°. One such section gave for 
one albite twin 16°, for the other 15°, the Carlsbad half, dis- 
tinguished by the shape of the section, the arrangement of the 
lamellae and avery slight but perceptible difference in double 
refraction in the position of equal illumination, gave extinction 
angles so nearly similar that the two are practically alike. In 
convergent light the section shows the exit of a negative 
bisectrix, but owing to the fineness of the lamella the hyperbolas 
are broken and the image does not permit one to say whether 
the bisectrix is centered or not. The presence of the quartz and 
the clearness of its contacts with the albite permit of the use of 
Becke’s method. Both in the parallel and crossed positions the 
quartz is always found to be the more strongly doubly refracting. 
All of these determinations point clearly to albite and a quanti- 
tative determination of CaO in the rock showed a mere trace of 
it to be present. The spaces between the albites are filled with 
quartz, which is at times in solid irregular areas; at other times 
in little grains; sometimes in micropoikilitic intergrowths with 
an alkali feldspar. There are also irregular masses of this feld- 
spar present, but they are rare. 
The whole character of this rock shows that it is of an alkali 
type and one in which soda predominates; it bears the same 
relation to ordinary syenite-porphyry that the Litchfieldite type 
of eleolite-syenite does to ordinary varieties. This character 
of the rock impresses itself sharply on the large phenocrysts 
mentioned above. While with low magnifying powers they show 
an even unstriated appearance, when examined with high ones it 
is seen that they are composed of a mingling of two kinds of feld- 
spar substances. They then present between crossed nicols on 
a gray background an excessively fine spotting of a material 
which has a somewhat higher double refraction, polarizing in 
higher tones of white. They recall sheets of iron which have 
been coated with zinc, or the frosting on a window pane, with a 
