240 ANNALS NEW YORK ACADEMY OF SCIENCES 



while at other times they drop out very gradually, so that the gradation' 

 from schist into "augen" gneiss is an almost imperceptible one. The 

 width of these belts varies from those less than a foot to those several 

 hundred feet wide. 



About two-thirds of a mile southeast of Bedford Village along the road 

 to Stamford, the "augen" gneiss is associated with a mica schist. In thin 

 section under the microscope, the schist shows a moderately fine crystal-^ 

 line texture and a distinctly foliated structure. It consists chiefly of 

 quartz, biotite and feldspar. The biotite is a deep reddish brown and is 

 oriented parallel to the foliation. The feldspar is mostly plagioclase 

 which gives extinction angles up to 30° in sections at right angles to the 

 albite lamellae. It is optically positive and is evidently an acid labra- 

 dorite. Some microline is also present. The quartz and feldspar occur 

 in irregular interlocking grains sometimes elongated parallel to the folia- 

 tion. Pyrite and a little apatite are also present. 



The "augen" of the gneiss consist of a pink feldspar twinned on tlie 

 Carlsbad law and reaching a length of over an inch. They are very often 

 rectangular in outline, although the ends are usually rounded. At other 

 times, they take on an elliptical shape. The long axes are usually ori- 

 ented parallel to the foliation, although not always so. "Augen" of white 

 feldspar showing albite twinning are also present, but they do not reach 

 as large a size as the pink ones. These give extinction angles up to 13° 

 in sections at right angles to the albite lamellae and are probably albite. 

 Beside the feldspar, fairly large grains of quartz sometimes appear in 

 veinlets with finer feldspar. In thin section, the pink feldspar is seen to 

 be mostly microline. At times it exhibits a perthitic intergrowth with 

 plagioclase. Quartz is seen in little veinlets throughout the rock. It 

 sometimes contains inclusions of rutile. The finer matrix of the "augen" 

 gneiss is very similar to the mica schist already described. It consists |0f 

 quartz, a deep brown biotite, feldspar, mostly microline, and a little mag- 

 netite. The structure is distinctly foliated. The "augen" gradually dis- 

 appear at the outer margins of the belt of "augen" gneiss which grades 

 into the schist. Where typically developed the "augen" constitute a large 

 percentage of the entire mass of the rock. 



Another specimen of the "augen" gneiss taken from a belt along a 

 road about one mile south of Bedford shows only a pink feldspar which 

 is nearly always twinned according to the Carlsbad law. The feldspar 

 is not as abundant as in the occurrence described above but is similar in 

 size, shape and orientation (PI. XT, Fig. 1). Small veinlets of peg- 

 matitic material parallel to the foliation are present. "Augen" of feld- 



