Through the kindness of Prof. B. Silliman, Jr. I have had the opportunity of examining another small collection, made by that gentleman, at the same locality. I consider the result of sufficient interest to warrant a special communication on the subject. The Fossils, though few in number of species, point unequivocally to the Miocene formation, the species being among the most familiar forms in the middle deposit of that formation in California. They were: Dosinia ponderosa, Saxidomus aratus, Conus ravus = _C. Californicus_ Reeve, Turritella Ocoyana Con., Natica, probably N. Recluziana, Pecten Pabloensis Con., Pallium Estrellanum Con., Carcharodon rectus Agas. a Balanus and one or two small shells too imperfect for determination. Mr. Moore presented on behalf of Prof. Dana, the following 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 crystallographic 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. [Illustration: FIG. 26.] Cleavage is perfect, parallel of the clinodiagonal section, or the plane _iì_; also distinct parallel to the line _cl_, as apparent often in the cross fractures of the crystals, and by occasional striæ. This plane of cleavage may be taken as the basal plane _O_. The planes _I_ and l 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 combination between two hemi-octahedral planes. In many of the crystals, only the right one of the two planes _I_ is present, and also only the left one of the two planes l. The prisms frequently terminate above in an irregular edge, made by the meeting of the one, or two, planes _I_, and the rough plane _r_, and this edge is sometimes cut off, more or less deeply, by a single oblique plane, which is one of the planes l. According to measurements with the reflective goniometer; _I_ : _I_ = 142° 26’ _I_ : _iì_ = 108° 47’ l : _iì_ = 101° 40’ I : l = 156° 20’ (approximately.) The inclination of the I on l 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 l:_iì_ would give, for l:l, 156° 40’.