294 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Referred to N4 the zone is incomplete and contains the extra forms 

 of ft ft 3, 5 and 8. 



X (7- 7- 14- 12). This pyramid was noted with the indices (5-5- 

 TO -9) by Hessenberg 8 on crystals from Maderaner Thai. According 

 to Irby, 9 Hessenberg's material was later shown to be dolomite from 

 Binnenthal. The present indices were substituted by Descloizeaux 10 

 for those of Hessenberg. The form must be regarded as quite doubt- 

 ful. 



(3 (7-7- 14-3). This is also a rare pyramid. It is shown in com- 

 bination in Fig. 51 of Zippe's n monograph where it is mentioned as 

 of uncertain authority. It lies, however, at the intersection of the 

 zones Z13 and [5723- 1010] both of which are well marked. Moreover 

 the term f is referable to normal series N5. The form seems to be 

 fairly probable. 



<5 (3361). This pyramid is given by Hauy 12 as occurring on crystals 

 from Derbyshire and Andreasberg. Zippe also shows a combination 

 (Fig. 50) from Andreasberg. On none of these figures, where the 

 zonal relations are susceptible of being checked by the drawing, does 

 the pyramid shown correspond to (3361), and in fact the drawing of 

 Zippe would make the pyramid in question (5-5-I0-1). (3361) 

 was also noted by Sansoni 13 on a combination from Andreasberg. 

 Sansoni's measured angles do not accord well with theory, there being 

 an average difference of 1^° between adjacent polar angles. The 

 form seems to be rather improbable. 



77 (5-5-I0-1). This pyramid was observed by Rogers 14 on crystals 

 from Frizington,_ England. It lies at the intersection of the well 

 marked zones [5502-3121] and [5051-5501]. The form seems to be 

 fairly probable. 



cp (8-8-16-1). This pyramid was recorded by Whitlock 15 on crys- 

 tals from Sommerville, N. Y. The zonal relations of this form are 

 not so good as those of (5-5-10-1) although it constitutes the limiting 

 member of the series (1121), (2241), 4481), (8-8-16-1). On the whole 

 this pyramid seems less probable than the preceding one and of about 

 the same degree of probability as (3361). 



8 Hessenberg, F., Min. Notiz., 4, Frankfurt (1861). 



9 Irby, J. R. Mc. D., Inaug-Disser., Goettingen (1878). 



10 Descloizeaux, A., Manuel de Min., Paris (1874). 



11 Zippe, F. X. M., Akad. d. Wiss. Wien. Math.-naturwiss. CI., 3 (1852). 



12 Hauy, Traite de Mineralogie Paris, Figs. 4, 72, 144, 152 (1S22). 



13 Sansoni, F., R. Accad. d. Line, 19 (1884). 



14 Rogers, A. F., Am. Jour. Sci., 12, 44 (1901). 



15 Whitlock, H. P., N. Y. State Mus. Memoir, 13, p. 74 (1910). 



