Granites of Cecil County, in North-eastern Maryland. 109 



equal in length and breadth, while others were columnar. 

 They usually show the rhombohedron at one end, the basal 

 plane modified by the rhombohedron at the other extremity. 

 All were strongly pleochroic, C light yellow, and in the direc- 

 tion at right angles to the principal axis, a deep brown. 

 These tourmalines contain a variety of inclusions, as magne- 

 tite, small stout crystals 

 resembling zircon, and 

 others which could not be 

 determined. The tourma- 

 line also forms inclusions 

 in the quartz. Irregular 

 cracks occur parallel to the 

 basal plane and rarely par- 

 allel to a prism, as shown 

 near the center of Figure 6. 

 A number of these hemi- 

 morphic crystals are shown 

 in Figure 6. Magnetite and 

 dodecahedral garnets are 

 less abundant than tour- 

 maline. Green hornblende 

 also occurs in prismatic 

 and cross sections. This 

 mineral was not noted in the thin sections. 



Most remarkable of all was the abundance of bright yellow 

 and reddish-yellow crystals, with parallel extinction, and 

 whose optical properties seemed to accord with those of 

 staurolite. These crystals are usually strongly pleochroic (see 

 Figure 6). It will be remembered that in the microscopical 

 study of this zone, the staurolite crystals were always com- 

 pletely altered to mica, even to the center. 



Fio. 6. — Crystals in the granite and staurolite 

 schist residues. Z, zircon : G, garnet, 

 T, tourmaline ; St., staurolite ; M, 

 magnetite ; A, apatite ; 

 Sp., sphene. x 80. 



