372 



University of California Publications. 



[Geology 



preliminary paper, and in particular its reference to the di- 

 trigonal l)i pyramidal group announced by him at the December, 

 1907, meeting of the Geological Society of America, chiefly on 

 the basis of the etch figures. Recently C. Palache and C. 

 Hlawatsch have independently arrived at the same conclusion, 

 the former 20 basing his conclusion on the hexagonal development 

 of the second order forms, (1120) and (2241) and the latter- 1 on 

 the same ground and from a consideration of the etch figures. 

 Hlawatsch also discovers 22 certain natural irregularities on the 

 faces of the negative (Louderback) pyramid which might indi- 

 cate a pseudo-trigonal symmetry (possibly orthorhombic hemi- 

 morphic trillings), but finally decides in favor of the trigonal. 



Crystal constants of benitoitc. The average angle (0001) A 

 (10T1) is given by Rogers as 40° 10'; Palache 40° 12'; Hlawatsch 

 40° 14', the value arrived at by the writer on his earlier material; 

 Louderback 40° 18'; Baumhauer 23 40° 19' 37%". These yield 

 c : «=0.7310 (for 40° 10') ; 0.7319 (P.) ; 0.7327 (II.) ; 0.7344 (L.) ; 

 0.7351 (B.). Palache apparently adopts the reference axes (G 2 ) 

 and gives p =.4879 corresponding to p =.4896 (L.) ; Hlawatsch 

 selects (Gj) and gives p =.8461 corresponding to p o =.8480 (L.). 



In his table of Goldschmidt elements (GJ Hlawatsch gives 

 c=0.7327 when, following Goldschmidt 's practice, it should be 

 c= 1.2690 s4 lg t— 0.10349, corresponding to the writer's c=1.2720. 



Crystal forms of benitoitc. The following table gives the 

 correspondences of planes reported on benitoite by the various 

 writers : 



-o Palache, C. Note on Crystal Form of Benitoite. Am. Jour. Sci. (4), 

 27 (1909). p. 398; also German translation with slight and unessential 

 additions, Zeit. fur Kryst. u. Min., 46 (1909), p. 379. 



2i Hlawatsch, C. Die Krystallform des Benitoit. Centralblatt fiir 

 Min., Geol. u. Pal., 1909, pp. 293-302 and p. 410. Also Zeit. fiir Kryst. u. 

 Min., 46 (1909), p. 602. 



22'ioc. cit., pp. 300-301. 



23 Baumhauer, H. Ueber die Winkelverhaltnisse des Benitoit. Cen- 

 tralblatt fur Min., Geol. u. Pal., 1909, pp. 592-594. Besults of measurements 

 on some very small crystals giving simple, good reflections.. 



24 The value given by Hlawatsch is, for (Gj), c, but it is Goldschmidt 's 



(JO) 



practice to use uniformly in his Winkeltabellen c and report it simply 



(i) 



as c. c=cV3. The value 1.2708 for apatite given in his Winkeltabellen is 



(i) do) 



therefore not a " Druckfehler, " as stated by Hlawatsch (loc. cit., p. 299) 

 and should appear as printed. 



