224 



PROCEEDINGS OP THE AMERICAN ACADEMY 



These crystals presented no new planes, and corresponded in their 

 crystallographic elements so closely with those given by Des Cloizeaux 

 that it seemed best to refer the planes to the same axial dimensions. 

 The measurements were made with a reflecting goniometer, having a 

 micrometer screw graduated to ten seconds ; but since the planes were 

 usually rounded or badly striated, the reading could only be accurately 

 made in comparatively few cases, and in the table below the best 

 angles have been indicated by heavy-faced type. 



(7= 87° 39'. c: J: a= 1.0378 : 1.1807 : 1. 



ORTHO-DIAGONAL ZONE. 



