Mineralogy and Geology. 415 



ing 1, 2, 3 atoms of chlorine replaced by bromine. The boiling-points 

 of the chlorid of silicon and of the bromid of silicon have been deter- 

 mined by Pierre, a most accurate observer, the first to be 59°, the latter 

 to be 153°; the difference is 94° ; whence it follows that in the bro- 

 mid of silicon 3 atoms of bromine are substituted for 3 atoms of chlo- 

 rine in the chlorid of silicon ; that the first is SiBr 3 , the latter SiCI 3 , 

 and that silica is therefore SiO 3 ; and consequently we must admit the 

 atomic weight of silicon to be 21-3, H being assumed =1« 



II. Mineralogy and Geology. 



I. Notes on the California Gold Region ; by Rev. C. S. Lyman, 

 (in a letter to one of the editors, dated Puebla de San Jose, March 27, 

 1849.) — From the western base to the summit of the range of the 

 Sierra Nevada, is a distance generally of a hundred miles, or more. 

 The western slope is broken and precipitous, and through the deep ra- 

 vines that abound, flow the numerous mountain streams that form the 

 tributaries of the Sacramento and San Joaquin rivers. The gold re- 

 gion is a longitudinal strip or tract from ten to forty miles in width lying 

 about midway, or a little lower, between the base and summit of the 

 range, and extending in length a distance of many hundred miles 

 active operations being already carried on through an extent of four or 

 five hundred miles at least. The gold mines near San Fernando in a spur 

 of the same range and which have been known and worked to some 

 extent for many years, are doubtless a part of the same great deposit. 

 On approaching the gold region from the valley of the Sacramento or 

 San Joaquin, soon after leaving the plain, the attention is arrested by im- 

 mense quantities of quartz pebbles, slightly rounded, and of the size of 

 Walnuts, scattered over the gentle elevations which form the western base 

 of the Snowy Mountains.* There is here but little soil — the earth is of a 

 yellowish red color, and nearly destitute of vegetation. Nearer to the 

 gold deposits the quartz pebbles become larger, and not unfrequentfy 

 boulders are noticed of considerable size. The quartz is so uniformly 

 associated with the gold, that even the most unscientific explorer would 

 pot think of looking for the metal where quartz did not abound. Pass- 

 ing up the mountains it is easy to tell when you leave the region of 

 gold from the sudden disappearance of the quartz. In August of last 

 year, in company with Mr. Douglass and others, I ascended from the 

 "Dry Digujngs" near the Rio de los Americanos, to within a few miles 

 °f the snow, enjoying in the highest degree the sublime scenery pre- 

 sented by lofty and precipitous mountains, separated from each oilier 

 b y dark/ deep ravines, and wooded with primaeval forests of towering 

 fir s and pines. The back bone of this mountain range is granite, the 

 several varieties of which constiiuted almost the only rock visible in 

 ^e last few miles of our journey. In descending we passed succes- 

 sively several forms of gneiss and other primitive and transition rocks, 

 till w : e reached the slate formation which prevails in this part of the 

 gold district. We penetrated on this occasion some forty or forty-five 

 roiles beyond the " dry divings," and after leaving the quartz twelve 

 °r fifteen miles up, scarcefy*a particle of gold was discovered. 



* See observations by J. D. Dana, [2], vii, 257, 261. 



