396 L. V. Pirsson—Phonolitic Rocks from Montana. 
The orthoclase and nephelite composing the pseudomorph are 
fresh and clear, save a slight incipient -kaolinization of the 
feldspar. Besides these minerals there are a few small included 
crystals of egirite and some small crystals of minerals to be 
noted later. aes 
Portions of these psendomorphs were obtained and carefully 
freed from any of the surrounding matrix, powdered and 
treated with dilute nitric acid. After filtering, the solution 
gelatinized readily on evaporating and gave a strong reaction 
for soda, while only a doubtful trace of potash was present. 
This proves that occasional small patches of isotropic substance 
are elther sodalite or analcite and not any original unchanged 
leucite substance. 
Pseudo-leucites of the character described above were first 
found in Brazil by Derby. Graeff* believed them to be inelu- 
sions of eleolite-syenite, but Hussakt showed that they were in 
all probability to be referred to original leucites, a conclusion 
which was confirmed by the studies of precisely similar ocecur- 
rences in tinguaite from Magnet Cove by J. Francis Williams.t 
Titanite.—This occurs rather rarely in small crystals about 
*5™™_ It has the usual characters. 
Afgirite-augite.—Phenocrysts of augite are very rare. A 
few of a green variety with deep green egirite borders have 
been noted 1 to 2™™ long. 
Sodalite.—The crystals are very fresh and do not show any 
signs of alteration or zeolitization ; a little infiltrated calcite in 
cracks is now and then seen. 
They are filled with interpositions of extremely minute crys- 
tallites which are perhaps egirite. They usually show by the 
arrangement of these a zonal structure. They are quite idio- 
morphic, and in the few cases where they touch orthoclase, 
they project into it with crystal boundaries. The small egirites 
of the ground-mass usually surround them in such a way as to 
form green wreathes. 
Orthoclase.—The large orthoclase phenocrysts are very rare ; 
they are quite fresh save for incipient kaolinization. 
The ground-mass 11 which these phenocrysts lie is made up 
of a felt of alkali feldspars in small lath-like forms and egirite 
needles. The structure is pronouncedly trachytic but has a 
strong fluidal tendency, especially around the large phenocrysts, 
about which the streams of microlites bend and twist. Between 
the feldspar microlites are small formless patches of nephelite 
which only very occasionally show a crystal outline. 
Fluorite—This is found scattered through the rock in 
* Jahrb. f. Min., 1887, vol. ii, p. 257. 
+ Ibid., 1890, vol. i, p. 167. 
t+ Arkansas Geol. Surv. Ann. Rep., 1890, vol. ii, p. 267. 
