THE PELHAM AND WILBEAHAM AREA. 53 



apophysis penetrating the saxonite: («) the white saccliaroithil portion 

 forming its extremity and nearest to the olivine; (h) the bhiish-white, <'oarser- 

 grained portion which formed the neck of the mass and passed into the gneiss. 

 For the former he fonnd the composition of anorthite, and for tlie latter 

 that of andesit(^ The latter portion, as it apjjroaches tlu^ coiumon gneiss, is 

 less pure than tlie other, containing much biotite, but with the microscope 

 the characters of anorthite were presented clearly by both varieties; here 

 and there, however, the larger crj-stals were very distinct and were clearly 

 andesite. The mass is like the feldspar accompanying the "fringe rock" 

 of the Chester emery bed. 



The portion called andesite ])y Shepard is compact to tine-granular, 

 translucent, bluish-white, fresh-looking, showing slight flesh color from the 

 abundance of small disseminated biotite crystals, and having seams and 

 irregular masses of Idack tourmaline scattered through it. Occurring 

 largely in the latter, and more sparingly disseminated in the feldspar, are 

 minute crystals of zircon. 



The iinorthite grains are often almost entirely single individuals; here 

 and there a few very fine distant twin laminae are interposed, but these 

 run out in a short distance, and in many cases the whole surface is covered 

 by distant laminte lying at right angles to each other. The maxinnun 

 extinction was 31° to 34°. 



Under the microscope the feldspar shows through a lacelike network 

 of brightly polarizing films or raveled-out scales of nuiscovite, and this 

 increases until in slides cut from seemingly quite fresh material the feld- 

 spar can scarcely be distinguished in the mat of mica scales. 



The biotite is optically uniaxial, and is often decomposed wholly or in 

 part, the sides being dissolved into a congeries of colorless scales, or the 

 change attacking one or several of the lamin?e and proceeding quite across 

 the specimen; and much of the new mineral has wandered out and surrounds 

 the biotite crystals in large spots, which, with reflected light, are seen to 

 sun-ound the remnant of the original crystal like a growth of glistening 

 white mold, and these white spots are visible to the eye all over the slide. 



The zircons are white, with a faint tinge of red and a high adamantine 

 luster, or deep amber color to pale red by reflected and reddish olive-green 

 by transmitted light. The white crystals are most regularly-formeil, long, 

 square prisms with sharp termination P and 3 P, and apparently 3P 3. The 



