26 [APPENDIX 



An impure talcose rock occurs at Point Lobos, which extends east for 

 one and a half miles. The works of the "Mountain Lake Water Com 

 pany" have been carried through a portion of these rocks, and the masses 

 of serpentine that have been elevated to the surface from the depth of 

 one hundred and sixty feet have exhibited an interesting feature in the 

 history of these rocks. It was found, on examination, that the strong 

 odor given off from these stones was composed of free Bromine and 

 Iodine ; it is very persistent, and specimens which have been exposed 

 to the air for nearly three months have not lost their odor. 



From the Presidio on the bluffs near the bay, slates and sandstones 

 are found in a much disturbed condition from intrusions of trap ; the 

 strata are much contorted and twisted, and tilted in every direction, the 

 inclination varying fron five degrees to vertically in very short distances. 

 These rocks, as yet, have presented no fossils in the immediate vicinity 

 of the city, but pass into tertiary sandstone, containing organinc remains 

 one mile west of Montgomery Street, San Francisco, where they may be 

 found forming the west point of the North Beach. 



South of the city and near Rincon Point, the trachytes appear with 

 small veins of quartz running through them and the adjoining slates ; 

 the latter having suffered considerable change in structure near the point 

 -of contact with the igneous rocks. Traces of carbonate of copper are 

 observable in this vicinity. 



Crossing the Bay of San Francisco from Presidio Point, the rocks on 

 the Saucelito side correspond with the primitive formations above de 

 scribed. The serpentine series continue for several miles up the bay, 

 varying in its mineral characters at short distances. At San Quentin 

 the rocks are schistose, and half a mile beyond, again passes into a mas 

 sive form, and contains actinolite in fan-like groups of crystals ; a mile 

 beyond this, the rock becomes hornblendic, and thence gradually pas 

 ses into a trap formation, containing well defined crystals of the latter 

 mineral. 



On reaching the northern shores of the Bay San Pablo the hills to the 

 north appeared rugged and conical, indicating a preponderance of the 

 volcanic rocks. 



The route traveled next, lay through the Counties of Solano and 

 Napa. It has been before remarked that the sand-stone on one side of 

 the Straits Carquinez was identical with that on the other, and the line 

 of dip in both will be found to correspond. These rocks are permeated 

 by minute threads of quartz, and contain considerable quantities of mag 

 netic sand ; in some cases the quartz viens acquire a thickness of one or 

 two inches, and have in several instances been found to contain gold, 

 while the sand-stone itself possessed this character in a limited degree ; 

 it is contained mechanically in these latter rocks, and in general will be 

 found as a local deposit only. Small quantities of this metal have been 

 found in the stone used for building in San Francisco, which were taken 

 from the quarries in the vicinity of Benecia. It is doubtful whether 

 these rocks would ever warrant mining explorations, except in those 

 locations where the quartz has intruded to a considerable extent. In 

 this case they would prove of sufficient value probably, for mining in 

 the rocks below the sand-stope, and would be governed by the same 



