40 NEW YORK STATE MUSEUM 



and the surrounding grains. Occasional small grains of a micro- 

 graphic intergrowth of quartz and orthoclase. Some of the ortho- 

 clase shows a microperthitic structure. 



In this connection there was studied, thanks to Professor Pirsson, 

 a thin section of the contact of an aplite dike in an anorthosite from 

 Grand Discharge, Saguenay, Quebec. This aplite differs from the 

 above only in that the quartz is less abundant and in smaller grains 

 relative to the orthoclase and microcline. Also, there is no micro- 

 perthite, and the orthoclase shows a tendency toward idiomorphism. 



The garnet rims themselves show no variation in any of the thin 

 sections of these specimens. They are entirely composed of pink 

 garnet, rarely showing good crystal faces, and no anomalies. They 

 are intergrown with and include grains of clear unstrained quartz. 

 The quartz and garnet together form almost complete envelops 

 about ferromagnesian cores. Their relations are illustrated in plate 

 i6B. A more comprehensive illustration showing both the labra- 

 dorite on the one side and the pyroxene on the other is given in plate 

 17A. 



The thin sections of the core within the rims show that it js com- 

 posed almost entirely of pyroxenes. These pyroxenes are pale green 

 in transmitted light and show pleochroism either from pale green 

 to pink or pale green to a very slightly darker green. Further exam- 

 ination shows that the pyroxene with the pleochroism to pink is 

 orthorhombic and answers to the description of hypersthene. The 

 other pyroxene is monoclinic and appears to be a variant of augite. 

 As the extinction angle is uniformly high it would seem that the 

 pleochroism is due to the presence of a ferrous iron (hedenbergite) 

 molecule, rather than of a soda (aegirite) molecule. Both pyroxenes 

 show in places good crystal faces. 



As accessory minerals in these pyroxenic cores, there are magnetite, 

 a small amount of alteration products : epidote, calcite, uralite, and 

 more or less interstitial, clear quartz. 



Plate 17B is a photograph of part of a section cut from what 

 appeared in the hand specimen to be a single crystal. It shows an 

 intergrowth of the hypersthene and the augite. The light-colored 

 areas over the entire photograph are augite, the dark-colored areas 

 hypersthene, and the black grains magnetite. 



It is of interest to compare these relations with the descriptions 

 of similar ones given by F. Zirkel in his paper on " Urausscheid- 

 ungen in rheinischen Basalten," (Segregations in basalts of the 

 Rhine), page 34. He says: "Extraordinarily clear are the inter- 



