174 



PROCEEDINGS OF THE CALIFORNIA 



The Fossils, though few in number of species, point unequivocally to the 

 Miocene formation, the speeies being among the most familiar forms in the 

 middle deposit of that formation in California. 



They were: Dosinia ponderosa, Saxidomus aratus, Conusravus=C. Califor- 

 nicus Reeve, Turritella Ocoyana Con., Natica, probably N. Recluziana, Pecten 

 Pabloensis Con., Pallium Estrellanum Con., Carcharodon rectus Agas. a Bala- 

 nus and one or two small shells too imperfect for determination. 



Mr. Moore presented on behalf of Prof. Dana, the follow- 

 ing paper : 



On the Crystallization of Brushite. 



BY JAMES D. DANA, L. L. D., PROFESSOR OF MINERALOGY IN YALE COLLEGE. 



The specimens of the mineral Brushite, which I have had under crystallo- 

 graphic examination, were received from Mr. G. E. Moore, the discoverer of 

 the species. 



The crystals are slender, prisms, not over a third of an inch in length. A 

 common form (containing all the observed planes), is shown in 

 the annexed figure. The prisms are monoclinic, and are often 

 flattened, parallel to the clinodiagonal, as here represented. 



Cleavage is perfect, parallel to the clinodiagonal section, or 

 the plane il; also distinct parallel to the line cl } as apparent 'often 

 in the cross fractures of the crystals, and by occasional strise. 

 This plane of cleavage may be taken as the basal plane 0. 



The planes / and 1 are brilliant, especially the former. The 

 oblique plane situated on the back side in the figure, and which 

 may be called r, is quite rough, owing to the oscillatory combi- 

 nation between two hemi-octahedral planes. In many of the 

 crystals, only the right one of the two planes / is present, and 

 also only the left one of the two planes 1. The prisms frequently terminate 

 above in an irregular edge, made by the meeting of the one, or two, planes /, 

 and the rough plane r , and this edge is sometimes cutoff, more or less deeply, 

 by a single oblique plane, which is one of the planes 1. 



According to measurements with the reflective goniometer ; 



101° 40' 



156° 20' (approximately.) 



The inclination of the 1 on 1 could not be accurately measured, on account 

 of the minuteness of the planes in the crystals, in which both planes occur, 

 and the want of perfection in the reflection. The angle obtained for 1 : ii 

 would give, for 1 : 1, 156° 40'. 



By measurement with a goniometer attached to a compound microscope, the 

 plane angle between the lines of cross cleavage, or cl, and the edge /: I 

 (which equals the inclination of on the orthodiagonal section, or a plane it) 



