276 eae General Notes. 
fractive mineral; calcite in small rhombohedrons; yellow- 
_ brown biotite intimately associated throughout with muscovite 
and calcite; and bipyramidal prismatic crystals of a colorless min- 
eral, with an extinction of g—-10° against the long axis. The 
varioles are composed of a central kernel of about the same com- 
position as the rock. Surrounding this is a zone sometimes of 
calcite, sometimes of quartz, in which the mica occurs. Towards 
its inner side the mica is arranged in concentric layers, with con- 
siderable calcite or quartz between. The central portion contains 
only calcite and mica. Toward the outer side the calcite dimin- 
ishes in quantity and the granitic materials take its place. The 
exterior portion of the variole is composed almost entirely of 
_ feldspar and quartz, in which the biotite is concentrically arranged, 
while the calcite occurs only in isolated grains and rhombohedra. 
The calcite is regarded as an original constituent, since it is found 
included in the other minerals, and the varioles are supposed to 
be concretions. Porphyritic hyperite, a rock of granitic 
structure, composed of plagioclase, hypersthene and diallage, 
with hornblende, apatite, titanic iron and a little biotite as acces- 
X sory constituents, is found at San Diego, Cal. Kroustschoff de- 
S scribes? the plagioclase as occurring both in the ground-mass a 
also`in porphyritic crystals. The latter are developed most 
prominently in the plane of the brachypinacoid. Analysis shows 
them to have the composition Ab; An, ——Herman and Rutley 
have been studying the devitrification products of glass, heated 
to a high temperature and allowed to cool suddenly, They 
c 
larly distributed, without reference to the cooling surfaces. In the 
3 a : b ioi « s 
fined circular or approximately circular boundaries, and arè 
-1 Bulletin de la Société Minéralogique de France, VIII, p. 132. 
; i Bulletin de la Société ioira ade. : : 
__ * Proceedings of the Royal Society. v. xxxıx. No. 239, p- 87- 
eS eS Se eT ee ee _ a 
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