CALIFORNIA ACADEMY OF SCIENCES. 9 



of the doubtful crystal. This direction, as before remarked, lies 

 in the acute angle of the morphological axes. 



As at once appears from an examination of the orthographic 

 horizontal projections given for each crystal, figured on Pis. I, II 

 and III, and of the linear projection PL IV, the faces on cole- 

 manite crystals are finely grouped in zones; moreover, with but 

 two or three exceptions (/\, a, B) each face occurs in two or 

 more important zones, thus materially aiding in its determina- 

 tion. The four most important zonal points in Fig. 11, PL IV, at 

 once strike the eye; and it is worthy of note that the zonal 

 point a = 1, b = contains so many traces, while the corres- 

 ponding point a = — 1, b = 0, contains but one, that of 

 A (— 2 P oo). 



On account of the perfect clinopinacoidal cleavage, many of 

 the crystals examined have suffered from careless handling. In 

 Figs. 1, 4, 6, 8 and 10, the large development of m (oo P oc) is 

 due to this cause. "Wherever m is observable as a natural sur- 

 face, it is exceedingly small, and in one case only, wanting abso- 

 lutely. 



n (oo P oo) varies in this respect with h (2 P oo), being fairly 

 developed when h is large, and very small or absent when h is 

 absent. 



H (oo P 3) and J (oo P I) were both observed but once, and as 

 adjacent faces upon the same crystal-fragment (Fig. 7, PL II). 

 Both are quite small, and give very poor reflections, whence the 

 discrepancies, that will be observed in the table on page 16, be- 

 tween the observed and calculated inclinations of these faces to 

 the others in the vertical zone. The observed angle H : J= 

 174° 8' agrees well however with its calculated value 174° 6' 50". 



2 (oo P 2) is wanting on but one crystal that is unbroken at its 

 orthodiagonal extremities; m ( oo P oo) is absent on the same 

 crystal. On the other hand, z is always very small and gives 

 poor reflections. On one crystal (Fig. 9, PL III.) the faces of z 

 and m were merged into a continuous curved surface. In no 

 other instance was any irregularity of development noticed about 

 this portion of the crystal; but as we shall see later, it is quite 

 marked in the region of the edge n (oo P oo) : h (2 P oc). 



