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PLATE IV 



Figs. 1 and 2. 



Aberdeen Granite. Magnification, 4*5 diameters. Fig. 1 taken 

 with polarized light ; fig. 2 with ordinary light. The large crystal 

 of rnicrocline of fig. 2, Plate III. is shown in lower part of field, 

 centrally. 



M, rnicrocline ; F, felspar ; 0, orthoclase ; Q, quartz ; B, 

 biotite ; M, muscovite. 



Generally the darkest parts of fig. 2 represent biotite. 



