ro6 'Hie American Geologist. February, ison 
Millstone Point, Stoney Creek and some minor localities, were dis- 
cussed. They were shown to be biotite-granites or biotite-muscovite 
granites of several varieties. Although they have nearly or quite tht- 
same mineralogy as the prevailing gneiss of the region, the attempt 
was made to establish their intrusive character, by their relations to 
the wall-rocks and by their peculiar inclusions of the basic hornblendic 
and biotitic schists. The remarkable development of pegmatytes that 
everywhere characterize the region was also discussed both as regards 
mineralogy and geological relations. The paper concluded with a 
general review of the granites of the Atlantic sea-board and showed 
that they were with few exceptions biotite granites. Such analyses as 
are available were used in illustration. 
Augite-syi-fiite near Loon Lake, New York. By H. P. Gush- 
ing, Adelbert College. An interesting section exposed in a railroad 
cut near Loon Lake, shows an intrusive rock which has caught up 
fragments of the Grenville series. The rock is related to the augite- 
syenites but the chemical analysis shows some unusual features. A 
large area of anorthosite mapped in Franklin county, N. Y.. the past 
summer, was found to grade into similar rocks on all sides, which 
are regarded as varients of the gabbro magma. They present a range 
from rocks of the acidity of granite to basic gabbros. 
On the Phcnocrysts of Intrusive Igneous Rocks; h.y L. V, 
PiRSSON, Yale University. The term phenocryst is a con- 
venient substitute for "porphyritic crystals." There are two kinds, the 
"single" and the "recurrent," the former of which is a mineral which 
does not occur in the ground mass also, while the latter does. The 
phenocrysts of extrusive rocks were not considered in this discussion. 
The author argues for but one period of crystallization, though its 
conditions are very complex. Of these conditions the chemical are 
fully as important as the physical, of the latter the viscosity of the 
magma and the rate of cooling have great influence on the result. 
Strong arguments were adduced to show that the phenocrysts are not 
"intratelluric," but that they, were formed in place after the intrusion 
of the rock. The following familiar facts constitute som.e of the argu- 
ments against intratelluric origin: (i), .\bsence of phenocrysts from 
contact zones: (2), they are sometimes lacking in dikes and sheets, 
when the parent laccolith abounds in them; (3), the microlites sur- 
rounding the phenocrysts have been pushed into their present posi- 
tion by the growing crystal and are not indications of flowage. The 
most abundant minerals have a tendency to develop at the expense 
of the others, but too great uniformity is not to be expected of na- 
ture. 
Geology of the Mica Deposits in the United States; by 
Joseph A. Holmes, state geologist of North Carolina. The 
deposits of commercial mica in the United States, though widely 
separated, are limited to a few districts. They have been worked to 
some extent along the Appalachian system of mountains in New 
