1897.] Petrography. 149 
Missourite, a New Leucite Rock.—The body of rock consti- 
tuting the core of one of the volcanic centresof the Highwood Mount- 
ains, Montana, is a new type of leucite rock named Missourite by Weed 
and Pirsson.* The rock isin the form of a stock intrusive in Creta- 
ceous shale. It variesin character in different places, but is of the 
same general nature in all. The coarsest grained variety is a-dark 
gray granular rock composed of grains of fresh olivine, of pale green 
augite, of brownish-yellow biotite, apatite and iron oxides embedded in 
perfectly clear leucite in formless masses. The composition of the min- 
eral is as follows: 
SiO, AlO, FeO, MgO CaO K,O Na,O H,O Total 
54.46. 2224 68 tr 10 1886 .70 _ 2.29 = 99.33 
A slight zeolitization has occurred in some of the leucite, the new pro- 
ducts being analcite and a new potash zeolite analogous to natrolite. 
An analysis of the rock yielded : 
SiO? Al,0; FeO; FeO MgO CaO NaO K,0 H,O TiO. P.O; BaO SrO SO; Cl Total 
46.06 10.01 3.17 5.61 14.74 10.55 1.31 5.14 144 .78 21 32 20 05 03 99.57 
This is very close to the composition of absarokite.‘ Since the structure 
of the missourite is penite, the author classifies it as the plutonic equiv- 
alent of the leucite basalts 
The Crystalline Schists of the Spessart. apap to 
Klemm the crystalline rocks of the Spessart,Germany, 
and schists of unknown age, with which are associated basic intrusive 
and effusive rocks and their tufis. The schists occur on the periphery 
of a great granite mass, dykes from which have intruded them. Among 
the foliated rocks are quartz-echists, m miom schiste, staurolite-echists, cale- 
silicate hornfels, limestone, d sandstones 
and graywackes. The biotite, ‘staurolite and other similar constituents 
exhibit no evidences of the action of pressure upon them, although the 
rocks in which they occur are highly schistose. This fact leads the 
author to conclude that the foliation of the rocks was imposed upon 
them when in aplastic state and not after they had become rigid. The 
amphibolites are thought to be metamorphosed tuffs. The granite is a 
biotitic variety with a foliation produced by pressure, but in this case 
as in the case of the schists, the foliation was produced before the rock 
finally solidified. In the character of its intrusion the granite is lacco- 
“Amer. Jour. Sci., Vol. II, 1896, p. 315. 
“Cf. AMERICAN NATURALIST, p- 299. 
* Zeits. deutsch. geol. Geo., XLVII, p. 581. 
