292 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



The arbitrary rulings by which "extra" forms are adjudged " well 

 established," : ' probable," " doubtful " etc., are briefly: 



1° The normal series in which the form first appears. 



2° Its relation to other and well established forms of the calcite 

 form system as established by zonal relations. 



3° The author's description of the form, whether curved, dull, 

 sharply defined, etc. 



Zone 1 — Dihexagonal Prisms. Symbol 



Using Bravais-Miller indices 

 the prism zone is as follows: 



k 

 K 



and suppressing the third term, 



Form 

 Symbol 



v 



1-v 



N 3 



5 h 



hoo 

 





 



10-1-0 

 1 



10 



1 

 9 



<r 



710 



1 



7 



1 

 6 



(J) (i) 



310 

 1 

 3 



1 

 2 



I 

 2 







210 

 1 

 2 



1 



1 



530 



3 

 5 



3 

 2 



2 

 3 ' 



J 

 760 



6 



7 



6 



(6) 



a 



110 

 1 



Referred to N3 the zone is incomplete and contains the extra forms 

 Yq-, 7 and f . Of these the two last belong in normal series 6 = Nq and 

 the first, jq, seems to be doubtful. 



