The entire lower jaw and teeth of a horse, the fragments of which I exhibit to the Academy, were taken by me from the face of the shore cliff of Mare Island, together with broken pieces of bones of other large quadrupeds. The teeth of an _Elephas_ had been found in the same place, a few weeks before, by Mr. Brown, the Naval Engineer, by whom my attention was directed to the place. The fossils occur in a stiff sandy loam, which rests on the eroded surface of the Tertiary or Cretaceous beds below. Near the surface is a layer of oyster shells, apparently an upraised bed, most of the shells being entire. The fact that the Horse and Elephant roamed together over our hills and plains, at the dawn of, or before the human period, is certainly not without interest. Ammonites or Ceratites from Oregon Bar, Middle Fork of the American River. BY PROF. WM. P. BLAKE. The specimen which I exhibit to the Society this evening, is from the collection of J. J. Spear, of this city. It was kindly loaned to me by that gentleman for examination. Not wishing to risk the specimen, by sending it to a paleontologist at the East, I had it photographed, and sent a copy to F. B. Meek, Esq., of Washington. It is not possible to determine from the specimen, whether these fossils are new or not, or even, whether they are _Ammonites_ or _Ceratites_. They appear to be not unlike the fossils described by Dr. Trask, under the name of _A. Chiceonsis_, Proc. Acad. Nat. Sci. Cal.; but it is not safe to identify them, without the septæ can be clearly made out. There are several casts in an argillaceous, somewhat micaceous slate. This locality is about 15 miles from Coloma. It is not certain, whether the specimen was taken from the slates in place, or broken from a loose mass. Mr. Moore presented the following paper: On Brushite, a new mineral occurring in Phosphatic Guano. BY GIDEON E. MOORE, PH. B. In the spring of the present year, I received through the kindness of Wm. E. Brown, Esq., of Mare Island, in this State, a specimen of a mineral discovered by him in a cargo of phosphatic guano, at Camden, N. J. The locality from which it was derived, is not known, and though letters of enquiry have been sent to the parties to whom the cargo was originally consigned, no reply has been received up to this date. The texture and appearance of the guano would, however, point to some one of the Caribbean Islands, and more particularly, to the Island of Sombrero, as its probable source. It is very probable that the mineral may be recognized among the crystallized products occurring in other guano deposits.