156 



Field Columbian Museum — Geology, Vol. III. 



in Fig. 3, PI. LIIL In calculating the forms the axial ratios estab- 

 lished by Stevanovic have been employed rather than those of Mohs. 

 These values are as follows: 



a :b : c = 0.5962 : 1 : 0.665 



= 90° 41' 



The following is a list of the forms observed on the Mercur orpi- 

 ment, those marked with an asterisk being new: 



In connection with these crystals the well-known crystals * from 

 this locality occurring in cavities in clay were examined. These 

 crystals are of smaller size and are for the most part obviously twins 

 but their planes were found to be so poorly developed that no satis- 

 factory measurements could be obtained. 



* App. Dana's Mineralogy, i8qq, p. so. 



