2r 8 j 7t_ 



mn ( 2 



110 T. L. Walker — Notes on Sperrylite. 



probabilities are represented by equations (3) and (5) respec- 

 tively, and is, therefore, equal to P . p, or 



2r 2r r 2 ) (m — x) (n—y) , 



— + - \ v V 2 l .dx.dy (6) 



3m 3n 4m?i ) m n a v ' 



Integrating the two expressions which make up equation (3) 

 between the limits x and x+Jx and y and y+Ay, respectively, 

 the above expression becomes : 



2r 2 j 7t 2r 2r r 2 ) z/cc/ 2x + Ax\Ay! 2y-\-Ay\ 



ran (2 3m 3?i 4mn ) m \ 2m / n \ 2?i /' 



which, for r = 1 mile, x — 2 miles, y — 2 miles, m = 10 miles, 

 n = 10 miles, and J;i and Ay each equal to 1 mile, becomes 

 -g-j^. That is, under the conditions stated, B would stand one 

 chance in 6173 of finding the shoal. 



Art. XIII. — Notes on Sperrylite ; by T. L. Walker. 



The interesting mineral sperrjdite was first described by 

 Professors Penfield and Wells in 1889.* Being a diarsenide 

 of platinum and crystallizing in pyritohedral forms, it serves 

 to link the platinum group of metals with the iron group, since 

 in the latter group diarsenides and disulphides commonly crys- 

 tallize in pyritohedral forms. In June, 1893, the writer 

 obtained permission from Mr. H. P. Mcintosh, secretary of 

 the Canadian Copper Company, to visit the Vermillion mine 

 in Algoma, Ontario, and to obtain specimens of sperrylite and 

 associated minerals. The notes here submitted are derived 

 from an examination of the material collected. 



Professor Penfield described four crystal forms on sperrylite, 

 (111), (001), (110) and tt(210), but he also adds : " Some crys- 

 tals appear to be somewhat rounded by other faces, but none 

 of the latter could be determined."! 



Some of the larger and more promising crystals were exam- 

 ined under the microscope. The common forms observed were 

 (111) and (001), generally in combinations in which the former 

 usually predominates. The form (110) was not recognized 

 on any of the crystals examined. 7r(210) could be seen on 

 most of the larger crystals, though the faces were generally 

 small. Another form was observed which replaces the angles 

 formed by (111), (001), and tt(210). The edges formed by the 

 intersection of these new faces with 7r(210) are parallel, and 

 hence the new form belongs to the same zone as 7i(210). The 



*This Journal, xxxvii, 67, 71, 1889; Zeitschr. f. Kryst., xv, 285 and 290. 

 f Zeitschr. f. Kryst, xv, 291. 



