1893.] Mineralogy and Petrography. 563 
spheroidal inclusions, that have been taken for Hussak* to be leucites. 
Kemp‘ has recently examined this rock very carefully, and now 
describes it as composed of biotite and pyroxene imbedded in an iso- 
tropic groundmass that is chiefly analeite. The biotite is dark brown 
and the pyroxene of a faint yellow color, with an extinction of 33°. 
The spheroidal inclusions are analcites, about whose ruins are often 
grouped grains of biotite and crystals of sphene. An analysis of one 
of the spheroids, after deducting 3.886 % of Ca Co,, gave: 
HO SiO, 1,0, Fe0, Ca0 KO Nao 
631 5244 2644 43 194 854 890 
As to the origin of the analcite the author is not certain. It may 
have been derived either from leucite, in which case the rock would be 
a leucite-tephrite, as considered by Hussak, or it may be alteration 
product of nepheline. 
A Sodalite-Syenite from Montana.—In the mountains form- 
ing the northern portion of Montana, Lindgren® and Melville have dis- 
covered post-cretaceous quartz-porphyrites, lamprophyres, augite- 
trachytes, analcite basalts, and a peculiar sodalite-syenite, somewhat 
resembling certain rocks described by Chrustschoff from Russia. The 
Montana syenite is from Square Butte, situated thirty miles southeast 
of Fort Benton. It is a light gray eruptive, associated with sheets of 
theralite and analcite basalt. Macroscopically it consists of lath- 
shaped feldspars, prisms of hornblende and pale brown grains of soda- 
lite. In addition, analcite and plagioclase are discoverable under the 
microscope. Many of the feldspar crystals are corroded in an extraor- 
dinary manner and the cavities thus formed in them are filled with 
-analcite which is believed to be an alteration product of albite. The 
hornblende is very dark brown, almost opaque, with a strong pleo- 
chroism, an extinction of 13° and a density of 3.437. Its analysis 
indicates its identity with the variety barkevikite : ° 
H,O SiO, Al,0,(TiO,) Fe,0, FeO NiO MnO CaO MgO Na,O K,O 
24 38.41 17.65 3.75 21.75 tr 19 10.52 2.54 2.95 1.95 
The sodalite is quite fresh. It forms irregular grains that are bounded 
by faces when in contact with analcite. It was evidently 
formed after the feldspar but before the analcite. The composition of 
3 AMERICAN NATURALIST., March, 1893, p- 274. 
t Amer. Journ. Sci., Apr., 1893, p. 298. 
5 Amer. Journ. Sci., June, 1893, p- 286. 
6 AMERICAN NATURALIST, June, 1890, p. 576. 
