EL/E0LITE-SYEN1TE. 



1 89 



the ordinary felspar. When the Nicols are arranged parallel to the 

 vertical and orthodiagonal axes of the felspar, that is when extinction 

 occurs, these zones around the black inclusions show a black cross 



n_>; 



N 



— N 



Fig. 1. — Opaque inclusions with polarising ** court " in micropertkite. 

 {Magnified by joo diameters.) 



distorted by strain ; when the Nicols are turned to the right 10 — 12°, 

 the upper right-hand and lower left-hand sectors of the zona extin- 

 guish. Similarly when the Nicols are turned 10— 12° to the left 

 the upper left-hand and lower right-hand sectors became dark ; 

 imperfect lamellar twinning is at the same time shown by the oppo- 

 site polarising sectors. The basal cleavage-cracks which cross the 

 orthoclase stop short at the edges of these zones around the opaque 

 inclusions. The phenomena are too regular and too clearly defined 

 for accidental strain phenomena, and are probably the result of the 

 development cf some other felspar around each opaque inclusion. 

 These inclusions are near the position of the minute interpositions 

 which characterise the schillerized variety murchisonite. Some .of 



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