574 The American Naturalist. . [June, 
SiO, TiO, Al,O, Fe,O, FeO MgO CaO Na,O K.O HO CO 
Rock 46.48 .99 16.16 6.17 6.09 +92 7-35. 5-85 3-08 4.27 .45 
Base 53.43 20.86 2.61 -29 1.14 11.63 2.51 7.06 
But little interest attaches to the components of the rock. The horn- 
blende and augite are often zonally developed. In the former the 
kernel shows evidence of having been corroded, while the external 
envelope never exhibits sign of such resorption. Analyses of one 
variety of the augite and of the hornblende appear in the paper. The 
latter mineral contains 3.37 per cent. of K,O. As the result of a 
microscopic study of the « Weissenberg gneiss,’’ in Saxony, in which 
cordierite and other characteristic contact minerals were discovered, 
Weber ë pronounces the rock a member of the graywacke series that 
has been metamorphosed by the Lausitz granite.—The basalt of Royat 
(Puy-de-Dome) contains geode-like cavities lined with calcite and 
other minerals, Calcite also fills crevices and holds fragments of the 
rock torn from the sides of the clefts. In some of these fragments 
are crystals of feldspar with the morphological and optical properties 
of orthoclase, but with a large proportion of sodium in its composi- 
tion (SiO, = 66.83 ; Al,O, = 19.20 ; CaO =.06; K,O = 6.29 ; Na,O= 
6.8).°——Zirkel? has determined the small hexagonal crystals in the 
altered sandstone of Steinberg, in the Habichtswald, Germany, to be 
cordierite, produced probably by the solution of the interstitial sub- 
stance of the sandstone by basalt. Termier ê notes the occurrence of 
veins of orthoclase and quartz in the silicified Carboniferous schists of 
Saint-Etiénne, whose structure is neither micropegmatitic nor micro- 
, Stanulitic, though both minerals were deposited simultaneously from 
the same mother-liquor, He also describes briefly a silicified schist 
consisting of bands of opal and chalcedony, from the Butte of Mont- 
_ ‘Taynand.—,-Quartz-twins occur porphyritically developed in the 
9 
pumice of Cobo de Gata. 
Miscellaneous.—Offret W has recently published a very exhaustive 
account of some investigations upon, the effect of various temperatures 
upon the indices of refraction of several minerals, for every color 10 
the visible spectrum, His paper opens with an historical review of the 
- Work already published. Then follows a very full description of the 
‘ Arnie Jahrb. J. Min., etc., 1891, L., P. 211. 
: eee Soc. Franc. d. Min., III., 1890, p. 372. 
Sf Min., ete., 1891, I., p. 109. 
Bull ranc. d. Min., XIII., 1890, p. 330. 
nn. Neues Jahrb. f. Min, etc., 1891, I., p- 108. 
`- 9 Osa 
10 Bull. Soc. Franc. d. Min., XIII., 1890, p. 450. 
