26o The American Naturalist. [April, 
The rock consists almost exclusively of a microcrystalline 
groundmass of quartz and albite in which are a few porphy- 
ritic crystals of the latter mineral. These are sometimes broken 
up into patches divided by narrow seams of feldspathic sub- 
stance with an extinction different from that of the albite. 
The analysis yielded : 
SiO, Al.OsFeA CaO MgO K,0 Na.O Ign. 
77.29 14.62 tr .38 .16 7.60 .57 
— Gonnard' mentions pyrite, oligoclase, emerald, garnet, 
beryl, calcite, chlorophyllite, apatite and tourmaline as acces- 
sory constituents of the gneiss occurring along the banks of the 
Saone near Lyons, France. — Kloos' has examined the thin 
sections of rocks that have been subjected to great artificial 
pressure, and finds in them no signs of mineral crushing. He 
advises care in ascribing to pressure the crushed appearance of 
minerals in rocks. He is inclined to regard the phenomenon 
as due to increase in volume under chemical change. — A typ- 
ical picrite occurring in boulders near St. Germans in the Lis- 
keard District in Cornwall, England, is mentioned by Bonney' as 
containing augite which has been ghanged successively into 
brown and green hornblende, and colorless needles of the same 
mineral, while the original form of the augite has remained. 
— Glaucophane has been discovered by the same author* as a 
secondary product of augite in a diabase occurring in a block 
in the Val Chisone, Cottian Alps. — Aggregates of topaz, a 
little feldspar, kaolin and mica have been found by Salomon* 
in a granular quartz rock (one variety of the greisen) resulting 
from the silicification of the granite at Geyer in Saxony. — The 
green-sand from just above the chalk beds in Kent, England, is 
composed*' of grains of quartz, flint, feldspar, glauconite, mag- 
netite, spinel, zircon, rutile, tourmaline and occasional grains 
of garnet, actinolite, epidote and chalcedony. — An eclogite 
from near Frankenstein in Silesia consists essentially' of om- 
phacite and a calcium garnet. The omphacite contains inclu- 
sions of smaragdite, and portions of the garnet have passed over 
into zoisite through the loss of calcium and the assumption of 
Bull. Soc. Frang. d. Min. XII. p. i 
■ Zeits. d. deutsch. geol. Gesell. XL. 
' "■ 1 Magazine, Oct. 1888. { 
■ Min. Magazine, Dec. 1887. p. 191. 
' Zeits. d. deutsch. geol. Gesell. XL. p. 570. 
' Miss. Gardiner: Quart. Jour. Geol. Soc. No 
' Traube : Neues Jahrb. f. Miner., etc. 1889. 
