Prof. Brewer gave an account of recent explorations in the Sierra Nevada, by the party connected with the State Geological Survey. The exploration extended from Kern River to the Yosemite Valley, and was peculiarly rich in scientific results. The crest of the chain is very high; along the whole of this distance, the high peaks, rising to above 13,000 feet, the culmination being between the sources of the Kern and Kings Rivers, where there are a number of peaks over 14,000 feet, and one about 15,000 feet in height. Along the whole of this, there are abundant traces of glaciers, some of the morains of which are truly gigantic, far surpassing anything else of the kind yet found in the State. The cañons of all the principal streams are very deep and abrupt. The Big Trees or Sequoias, were found over a large area, extending perhaps 25 miles along the western slope, along the tributaries of the San Joaquin, Kings, Kaweah, Tule and Kern Rivers. The amount of snow in this part of the sierras, is apparently very much less than usually occurs. Prof. Wm. P. Blake, read the following: Note on the discovery of Fossils in the Auriferous Slate formation of the Mariposa Estate, California, and the probable geological age. BY PROF. WM. P. BLAKE. During a recent visit to the Mariposa Estate, Mariposa County, my attention was called to some organic remains in the slates, near Bear Valley, by Miss Errington, a lady who takes an enthusiastic interest in the sciences of geology and mineralogy, and has for some time past, been seeking for fossils in the gold formation of that neighborhood. One of the specimens was the cast of a bivalve shell, and appeared to me to be a _Plagiostoma_. On further search, we found other specimens, some of which much resemble _Inoceramus_, to which I am inclined to refer them. Certain long tubular cavities in the slates, marked with heavy lines, and slightly converging, seemed to be casts of long, nearly cylindrical shells, possibly _Nerinæa_. These forms would indicate a Jurassic or Cretaceous age for the formation. I propose to submit these specimens to a competent Palæontologist, at the East, for examination, and to dedicate one of the species, if new, to Miss Errington. REGULAR MEETING, OCT. 17TH, 1864. President in the Chair. Seven members present. Donations to the Cabinet; A fossil tooth of Elephant, and several fossil teeth of Horse, from Wellington’s Station, on the road from Carson Valley to Aurora, by Mr. Clayton. Specimens of silver ore from the Osceola Lode, Montgomery District, 60 miles S.E. of Aurora, and specimens of silver ore from Bear Mountain, Calaveras County, by Mr. Clayton.