Mineralogy and Petrography. 
(General iJ^otes, 
MINERALOGY AND PETROGRAPHY. i 
Petrographical News. — An article full of interesting observa- 
tions on the alteration of olivine and augite, is by Dorr,^ who describes 
the minettes, kersantites and melaphyre dykes in the neighborhood of 
Dresden, in the Plaunischer Grund. The three rocks cut syenite, and 
the first two contain inclusions of it. The olivine of the minette is 
frequently twinned parallel to P^. It has often changed into pilite 
and talc, and has, in some cases, been pseudomorphed by quartz. 
The augite has given rise to pseudomorphs of calcite and quartz, 
and has undergone alteration into biotite under the influence of 
dynamo-metamorphism. The biotite, some of which is primary, 
has been enlarged since the solidification of the rock. It is inter- 
grown with orthoclase in some instances, and alters into chlorite and 
talc, with the addition of rutile in the minettes, and of anatase in the 
kersantite. The quartz inclusions in both rocks are surrounded by 
rims of green augite, while inclusions of orthoclase have altered on 
their edges to biotite when solution has not been completed. When 
the fusion has proceeded to completion, no evidence of the former 
existence of the inclusion is present. The paper is well illustrated, and 
It contains full literature of the most important points discussed. 
Bonney3 has made two traverses across the crystalline rocks of the 
Alps with the object of determining their age. In the course of his 
article on the subject he describes the microscopical character of the 
gneisses, mica-schists and clay slates found there. A mica-schist from 
the Octroi de Vizille consists of mica, cyanite and quartz. The 
cyanite occurs in irregular-shaped grains, containing tiny flakes of 
brown mica, black granules and minute belonites. Calci -mica-schists 
from the eastern side of the Cottian Alps are composed of granular 
quartz, calcite, and brown and white mica. These are supposed to have 
originated from sediments. The other rocks described present no 
peculiar features, except that they all exhibit the effects of crushing 
'Edited by Dr. W. S. Bayley, Colby University, Waterville. Me. 
""Miner, und Petrog. Mitth., XL, p. i6. 
^ Quart Jour. Geol. Sac, Feb., 1889, p. 67. 
