298 PROCEEDINGS OF THE AMERICAN ACADEMY. 



well marked, containing at least four poles of well established forms, 

 would seem to remove any doubt as to the validity of this form. 

 Between (13- 0-13-1) and (1010) the forms are: 



Referred to N 4 this portion of the zone is incomplete and contains 

 the extra forms 18, 20, and 24. 



v. (18-0-18-1). This rhombohedron was observed by vom Rath 22 

 on crystals from Lake Superior and subsequently by von Foullon 23 

 on crystals from Arlsberg. Goldschmidt 24 regards both observations 

 as doubtful and substitutes the form (19-0- 19-1) as both conforming 

 better with the rhombohedral series and agreeing more closely with 

 the recorded measurements. 



i. (20- 0-20-1). Sansoni 25 records this rhombohedron from St. 

 Blasien, Baden. The form is very close to (22-0-22-1) which is 

 recorded by the same authority from a neighboring locality, under 

 what appears to be similar conditions. The form is quite doubtful. 



C. (24-0-24-1). This rhombohedron was observed by Hobbs 26 

 on crystals from Mineral Point, Wis. The form was identified from 

 one series of measurements, the difference in calculated angle between 

 (24-0-24-1) and (22-0-22-1) being 14'. It is possible that the 

 observed form should have been referred to the simpler indices. 



22 vom Rath, G., Pogg. Ann., 132, 387 (1867). 



23 von Foullon, H., Jahrb. geol. Reichs. Wein, 35, 47. 



24 Goldschmidt, V., Index der Krystallformen, 1, 378 (1886). 



25 Sansoni, F., Gior. d. Min., 1, 299 (1890). 



26 Hobbs, W. H., Univ. Wis. Sci. Ser. Bull., 1, 115 (1895). 



