1885.] Mineralogy and Petrography. 1215 
ogists and collectors.! F. Rinne concludes that crystals of 
milarite, which are apparently hexagonal, were really so at the 
time of their formation, and that their molecular disturbance is 
due to a subsequent change of conditions, as is true in the case 
of leucite and boracite.? 
PETROGRAPHICAL News.—The second part of the second vol- 
ume of Professor J. Roth’s Allgemeine Chemische Geologie 
has just appeared. This treats of the younger eruptive rocks, 
and especially on account of the wonderful completeness of its 
literature references, will form, as do the other parts of the same 
work, a most valuable addition to the library of every working 
geologist and mineralogist. A very concise elementary text- 
book of microscopical petrography has recently appeared, by 
Professor A. von Lasaulx, of Bonn. In spite of its small size it 
brings the essential points of this rapidly developing science down 
to date, and is especially to be recommended for its full bibli- 
ography.—In his recent exhaustive optical study of the mineral 
leucite, Professor C. Klein, of Göttingen, describes in some detail 
a new and very complete mineralogical and petrographical micro- 
scope, which is constructed by the well-known firm of Voigt & 
Hochgesang, of Gottingen.‘ This instrument, of which a cut is 
ee given in their latest catalogue (1885), may be had for 800 marks 
- ($200), andis undoubtedly the most satisfactory microscope in 
the market for the especial uses for which it is intended. 
Becke, of the University of Czernowitz, contributes a paper o 
the twinning of rock-forming pyroxene and amphibole.’ He 
finds in certain Hungarian pyroxene andesites that the bronzite 
crystals are frequently grouped i in radiating groups, in accordance 
with three anng laws, viz: twinning planes I, Pa (vom 
Rath); 2, 2P%, and 3, iF o The first of these is the most 
common and corresponds. very closely to the twinning law for 
augite, twinning plane P2. The frequently mentioned twins of 
augite and hornblende in rocks, with a composition—face apparent- 
ly inclined to the vertical axis, the writer follows Mr. George F. 
Becker® in considering merely ordinary twins, parallel to œ P 3, 
which are cut in the section parallel to some pyramidal face. 
J. H. Kloss, of Karlsruhe, has made some interesting contribu- 
tions to the subject of secondary hornblende in rocks.” He finds 
abundant evidence of compact as well as fibrous hornblende 
(uralite) originating from the paramorphosis of pyroxene, and can 
1 Das mineralogische Museum sap? Kaal. ie eee Berlin, 1885. 
3N hrbuch für Min., etc., 1555. 
3 noel en è in dii Geste sieme: Ein. Leitte für den akademischen Unter- 
215. 5- 
| 1835. 
= 6 Geology of the Comstock Lode. Monographs U.S. G S., Vol. 11, p. 113, pl. 
2 dd aoe Jahrbuch fiir Min., etc., 1885. 1, p. 82. Versammlung deutscher Natur- 
forscher und Airtze in Strassburg. Sept. 18-23, 1885. 
