184 PROCEEDINGS OF THE CALIFORNIA 



are nephiline ; so perfect is their transparency, that at first I concluded that 

 they were Iio'.cs where the rock iiad been ground out ; but on using polarized 

 light, I discovered they were doubly refracting crystals. I am not aware that 

 any of these compound rocks have been found in such small prisms. Some 

 of the smaller prisms measure not more than 0.10 in. across, and in the speci- 

 mens I liave some three to four inches long. There can be no doubt but that 

 originally they were aggregated into masses, and that their separation is the 

 result of weathering ; in fact, amongst my specimens are some in which many 

 prisms are still attached to each other. The locality from which they were 

 collected was at Black Rock, in the State of Nevada, but I did not collect 

 them myself. I found them here, they having been sent down as tin ore. On 

 account of the roughness of their surface, caused by weathering, I have been 

 unable to measure their angles. 



Dr. Gibbons remarked on the waves of temperature which seem 

 to range from S. E. to N. W. along the coast of this State, south 

 of this city, following its trend, while they run nearly on the me- 

 ridian lines further inland. 



Professor Whitney gave an account of the investigations carried on during 

 the progress of the Geological Survey of California, having for their object the 

 determination of the value of the barometor as a hypsometrical instrument, the 

 expectation being that, after a sufficient stock of observations shall have been ac- 

 cumulated and reduced, it will be possible to designate the hours of the day 

 for each month, when the results will approach nearest to the truth ; and in 

 general, to give practical rules in regard to the times of observing and the 

 method of reduction, the following of which will secure a closer approximation 

 to accuracy than can now be attained. 



An elaborate series of observations with this end in view was begun on this 

 coast, some ten years ago, by Col. R. S. Williamson, of the U. S. Engineers ; 

 but the work was suspended by the Engineer Bureau just before being com- 

 pleted. Col. Williamson's results, however, were published in the form of a 

 superb quarto volume, as an " Engineer's Paper," and this contains a large 

 amount of valuable material ; so that the work of the Geological Survey is only 

 to be looked upon as supplementary to that so ably commenced by him. 



The stations at which observations are being carried on at present, under 

 the direction of the Geological Survey, are along the line of the Central Pa- 

 cific Railroad, and their elevations are presumed to be accurately known from 

 the levellings of the railway surveyors. The points selected are San Fran- 

 cisco, Sacramento, Colfax and Summit, approximately 0, 30, 2400 and 7000 

 feet above the sea level. The observations have' already been continued at 

 these points nearly a year, and are made at the Smithsonian hours — 7 A. M., 

 2 P. M. and 4 P. M. The greatest care has been taken that the instruments 

 should be kept in perfect order, well-placed for accurate results, and carefully 

 and punctually observed. The observations of the past ten months have 

 already been partially worked over by Professor Pettee, of the Geological 



