1889.] Mineralogy and Petrography. 
A little south of Murfreesboro, in Pike county, Arkansas, is a mass 
of peridotite of Cretaceous age, whose microscopical features have 
recently been examined by Dr. R. N. Brackett." The rock consists 
of porphyritic crystals of colorless olivine and brown mica in a 
ground-mass composed of lath-shaped crystals of augite, little crystals 
of peropskite and grains of magnetite in a decomposed yellowish 
glassy base. The rock is similar in many respects to the only other 
two peridotites described from the United States. It is placed by the 
author in the group of kimberlites or picrite-porphyries of Lewis. 
The ore-bearing rock at the Treadwell gold mine in Alaska is, accord- 
ing to F. D. Adams, '3 u a hornblende granite, much crushed, altered 
and impregnated with secondary quartz, calcite and pyrite." This in- 
cludes kernels of more compact granite in which alteration has not 
proceeded so far. Much of the gold present in the rock occurs free 
in the pyrite. The rock is interesting in that it contains original 
epidote. Interesting intergrowths of the rare mineral allanite and 
epidote are described in some detail by Dr. Hobbs ^* in a porphyritic 
granite at Ilchester, Md., and by Lacroix*' in the pyroxene-am phibole 
gneiss of Finisterre, in the pyroxene-wernerite gneiss of the Lower 
Australian Waldviertel, and in the scapolite-gneiss of Odegarden in 
Norway. These intergrowths (in the Ilchester rock) consist of an 
idiomorphic core of brown allanite, zonally developed, and around it 
an idiomorphic or an allotriomorphic mantle of pale yellowish green 
epidote. In the allanite the axis of elasticity is inclined at an angle 
of 36° to the vertical axes, while in the epidote this is only 3°. 
Analysis of the purified epidote yielded Dr. Hildebrand : 
SiO, FePj.FeO MnO CaO MgO Hp P.O. TiO^ 
37.63 15.29 .31 22.93 .31 2.23 .44 3.78 
Dr. Hobbs regards the epidote as secondary in the Ilchester rock, 
while Lacroix thinks it primary in all the occurrences described by 
Mineralogical News. — In a short paper forming an appendix to 
his notes on the minerals occurring in the neighborhood of Baltimore, 
Dr. Williams*^ briefly mentions fifteen new species that have been 
^■^ Amer. Jour. Sci., XXXVIII., July, 1889, p. 56. 
1* Amer.Jour. Sci., XXXVIII., Sept., 1889, p. 223. 
15 Bull, de la Soc. Franc, de Min.,YA\., 
