1895.] Petrography. 1081 
of the original rock. A second type of imandrite resembles a silicified 
porphyritic rock. A hypersthene-cordierite-hornfels, with handsome 
cordierite crystals, an oliving-actinolite schist, containing cordierite, 
and several contact metamorphosed sediments are described in detail. 
The major portion of the article deals with the nepheline syenites and 
the related rocks—theralites, augite,-porphyrites, iolites, monchiquites, 
tinguaites, etc., and the new rocks, lujavrite and tawaite. The thera- 
lite agrees exactly with Rosenbusch’s definition of the type. It isa 
medium grained aggregate of idiomorphic pyroxene, and granitic 
plagioclase and nepheline, with the accessories brown hornblende, bio- 
tite, sphene, magnetite, apatite, sodalite and secondary zeolites. Luja- 
vrite is a trachytic nepheline-syenite with its components largely idio- 
morphic. Tawaite is a coarse-grained mixture of sodalite and pyrox- 
ene. 
Around the periphery of the nepheline syenite the rock is different 
from its main mass and it has produced contact effects with surround- 
ing rocks. A nepheline syenite with a trachytic structure is described 
among the peripheral phases of the syenite, and a rock resembling 
pulaskite, but containing no porphyritic crystals. This rock, which 
the authors call umptekite, is a nepheline syenite, poor in nepheline, 
It differs from the nepheline syenite in containing a calcium-feldspar, 
from augite-syenite in possessing hornblende instead of augite, from 
laurvikite in its structure, and from akerite in its lack of quartz. Its 
structure is granitic. Arfvedsonite is its principal amphiboloid, and 
besides, it possesses aegerine. The characteristic minerals of the 
nepheline syenite are also present in it. The aegerine is frequently as- 
sociated with sodalite or with feldspar in pegmatitic intergrowths. A 
sillimanite gneiss is mentioned as possibly being a metamorphized sed- 
iment. 
The Matrix of Naxos Corundum.—The corundum‘ of Naxos 
occurs in an iron gray foliated or massive granular rock composed al- 
most exclusively of corundum and magnetite. The first mentioned 
mineral is in largest quantity. Associated with these two components 
are limonitic and hematitic alteration forms of magnetite, margarite, 
tourmaline, muscovite, cyanite, staurolite, biotite, rutile and occasion- 
ally spinel, vesuvianite and pyrite. The corundum is in rounded 
grains or in well defined crystals surrounded by magnetite. Most of 
the other constituents, with the exception of the magnetite, appear to. 
be the results of shearing. An analysis of the rock gave: Corundum 
*Tschermak, Min. u. Petrog. Mitth., xiv, p. 311. 
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