296 PROCEEDINGS OF THE AMERICAN ACADEMY. 



are sufficiently simple to mark such zones in any way. The form as 

 a hypothetical one should be rejected. 



(8-8-16-9) = (11 -3-5). This hypothetical pyramid like the pre- 

 ceding one should be rejected, for the reasons given above. 



Zone 3 — Positive Rhombohedrons. 



c h 



Symbol j. 



The most prominent forms in the zone of the positive rhombohe- 

 drons are (1011) and 4041). These forms should certainly be re- 

 garded as knot points. Between (4041) and (10T0) the two most 

 prominent zone intersections are (7071) and (13-0- 13-1), both fairly 

 common forms. Dividing the zone in this way we have for the first 

 portion : 



Form 

 Svmbol 



N 3 



Referring this series to N3 the series is incomplete and contains 

 the extra forms f- and § both of which would fall in normal series N4. 



g. (4047). This rhombohedron was observed by Hessenberg (loc. 

 cit.) on crystals from Maderaner Thai; it had previously been re- 

 garded by Zippe 16 as doubtful. As pointed out under x (7 • 7 • 13 • 12) 17 

 Hessenberg's specimen proved to be dolomite from Binnenthal. The 

 form in question lies in the zone [ll02-1780] as well as in two less 

 well marked zones and may be regarded as fairly probable. 



V (4045). This rhombohedron was observed by Sterrett 18 on 

 twinned crystals from the Joplin region. Although the form was 

 noted on a number of crystals, in the instance of only one crystal 

 could reflections be obtained. The form seems less probable than 

 (4047). 



The forms between (1011) and (4041) are: 



16 Zippe, loc. cit. 



17 See page 294. 



18 Sterrett, D. B., Am. Jour. Sci., 18, 73 (1904). 



