182 
CONTRIBUTIONS TO THE GEOLOGY OF MAINE. 
[BULL. 165. 
composition Ab 5 An 3 , and is therefore andesine (see fig. 11). The most 
common alteration is a clouding by means of myriads of minute specks 
of pure white analcite, which is distributed without order along cracks 
or in the center, or as a zone surrounding the crystal. The feldspar 
also shows chlorite or serpentine along the cracks, or may be striped 
by alternate bands of chlorite and calcite. 
A whitish isotropic mineral, with low refraction and birefringence 
abundantly present in the rock, suggested leucite," sodalite, and analcite. 
In order to determine which of these minerals was present, a portion 
of the rock powder was treated with dilute nitric acid and then filtered, 
and the filtrate yielded gelatinous silica so easily and abundantly that 
the mineral could not be leucite. A test of a portion of the original 
filtrate showed no chlorine, which the presence of sodalite would 
demand. Moreover, the rock yields water abundantly below red 
Fig. 11. — Optical measurements of a plagioelase crystal. 
heat in the closed tube. Analcite is the only rock-making mineral 
which corresponds in composition and optical behavior to the one 
under discussion. 
The analcite of the teschenite is either pure white or clouded by dust 
particles, and the slight birefringence is accordingly variable. It occurs 
abundantly in the typical slides, filling the polygonal areas between the 
interlacing feldspars, or filling cavities partly bounded by crystal faces, 
or as the secondary product described above. No alteration to second- 
ary minerals, as has been recorded by Fairbanks, was observed. The 
disputed question of the origin of the analcite in rocks of this class 
finds no additional evidence here, but the writer believes, with Rosen- 
busch 1 and Fairbanks, 2 that it is secondary probably after nepheline, 
and not primary, nor secondary after feldspar, as maintained by Rohr- 
back. 3 
1 Rosenbuscb, Mikrosk. Phys. der mass. Gesteine, p. 253. 
2Fairbanks, Bull. Geol. Dept. Univ. California, Vol. I, p. 284; Vol. II, p. 27. 
3 Rohrbach, Ueber die Eruptivegesteine im Gebiete der Schlesich-Mahrischen Kreideformation: 
Tscbermaks Mittheilungen, 1886, Vol. VI, p. 31. 
