-1:20 Pogae and Gohhehmidt — Quart:: from Alexander Co. 



out further harm to the specimens by the aid of the same 

 grinding goniometer ; whereby an oriented plane parallel to 

 the base was prepared upon the lower end of each crystal, 

 yielding when sliced off and polished an accurate basal section, 

 examinable under the microscope. 



Crystal 1 showed itself as right-handed quartz ; crystal 2 as 

 left-handed quartz. This determination is in agreement with 

 the ride* that the nature of light rotation in quartz may be 

 deduced from the relative positions of the trapezohedrons. Thus, 

 in right-handed quartz the trapezohedron faces, both + and — , 

 lie to the right of +10 ; and reversely, for left-handed quartz, 

 the trapezohedron faces are to the left of + 10. These 

 relations for each crystal are clearly brought out in the gno- 

 monic projections (figs. 3 and i). 



U. S. National Museum, Washington, and 

 Heidelberg, Germany. 



* See Des Cloizeanx, Manuel de Min^ralogie, Paris, 1862, vol. i, p. 15. 



