562 The American Naturalist. [June, 
MINERALOGY AND PETROGRAPHY:. 
The Petrography of the Abukuma Plateau, Japan.—The 
northern half of the Japanese Archean area, the Abukuma Plateau, is 
thought by Koto? to consist of a series of Laurentian granites and 
“pressure gneisses, cut by younger granites and other eruptives, and 
overlying these a series of schists, divided by the author into lower and 
upper Huronian. The Laurentian granitic are an older amphibole- 
biotite variety and a younger, intruding biotite granite. The former 
contains, in addition to the usual granite components, microcline, 
and a bluish-green, weakly pleochroic hornblende, that very frequently 
plays the role of an ophitic groundmass for the other constituents. 
This granite passes by dynamo-metamorphism into foliated phases, in 
which the various minerals have been compressed, and the quartz, in 
addition, granulated. The Huronian (?) beds are principally schists 
and gneisses, that differ from the Laurentian gneisses in having the 
plane parallel structure, i. e., they are composed of bands of different 
composition. The most important schists of the lower division are: 
gneissic mica schists, containing andalusite and sillimanite, two-mica 
schists, one of whose constituents is margarite, garnet-biotite schist and 
hornblende schist. A peculiar member of the series is a titanite 
amphibole schist, consisting of bands whose structure is granular. Its 
black bands are made up of green-hornblende, plagioclase and a little 
biotite, and its white ones of sphene and granular sahlite in a ground- 
mass of altered feldspar. The upper Huronian seriesembraces foliated 
amphibolites, mica-schists, and green schists that may be tufas. The 
distinction between the lower and upper members of the group seems 
to be based mainly upon petrographical characteristics. Among the 
rocks cutting these various schists may be mentioned an amphibole- 
picrite, pegmatites, and several varieties of diorite-porphyrite. 
The Leucite-Tephrite of Hussak, from New J ersey.—The 
eleolite syenite eruption of Beemerville, N. J., was accompanied by 
basic extrusions now represented by the smaller dykes associated with 
the large eleolite-syenite dyke in this region. One of the most interest- 
ing of the basic dykes is the one at Hamburg, Sussex Co. It is from 
15 to 20 feet wide and consists of a dark, tough, biotite rock, holding 
‘Edited by Dr. W. S. Bayley, Colby University, Waterville, Maine. 
? Jour. Coll. Science, Imperial University, Japan, v, 3., p. 197. 
