48 IGNEOUS KOCK — GOLD PLACERS — FOSSILS OF THE SANDSTONE. 



Sequoia flourish down evea to the level of the sea, a point much below the usual altitudes com- 

 mon to those trees. 



There the granite is nearly five miles broad, where it dips under the alluvium forming the 

 low land around the inner harbor. Southward it extends in a line southeast, forming the chief 

 mass of the mountain, occupying its western and highest ridge until it reaches the river San 

 Antonio. East of the granite lies a great width of serpentine rock running parallel with the 

 granite and forming a sharp, narrow crested ridge, which, by its abruptness upon the Salinas, 

 hides the main granitic ridge from view when travelling along that river. Still, the presence of 

 the granitic rock is revealed by the wash of almost every mountain stream which carries down 

 a large portion of primary rock among its debris. On the east of the serpentine lie talcose and 

 chloritic slates, intersected by filamentous veins of quartz. These being the mineral conditions 

 under which gold is found, it was suspected that the precious metal might be found in this 

 range ; in the winter of 1354-'55 prospecting was carried on to a small extent on the head- 

 waters of the San Antonio, in the northern part of San Luis Obispo county. A few native 

 Californians commenced washing there, and obtained about $4 per day for each hand ; the quan- 

 tity, however, ultimately obtained was but small, and the washings were abandoned after a 

 little. The protrusions of serpentine and magnesian slates drop down before the range 

 approaches San Miguel mission, and do not reappear again. The fossiliferous sandstones with 

 dosinia, underlying the Salinas river, rest on these, have been upraised by them, and are 

 in i:)laces rendered metamorphic by contact. The granite itself drops down, as stated, 

 and while diminishing in height covers a greater breadth to the east. Owing to the close 

 approach of the magnesian rocks to the river valley, the trail is obliged to leave it and 

 cross the eastern portion of the range, where it meets with the San Antonio river, which 

 rises in the granitic hills further north, and passes in the small trough between the serpentine 

 and granitic ridges of the mountain ; this trough is filled up by the fossiliferous sandstones 

 which here dip to the southwest, being influenced by the serpentine upheaval rather than by 

 the granitic, the latter being the rock first elevated. The sandstone is in places converted into 

 a rock resembling novaculite, and near the Mission Solidad beds of jasper and reddish porphy- 

 ritic rock are found. Angular fragments of prase occur in the arroyos which found their 

 vray into the valley ; a bed of conglomerate lies below the sandstones ; this stratum is of a 

 greenish tint, and contains pebbles of hyaloid quartz, prase^, serpentine, and porphyry. It was 

 not fully exposed, so that not more than 40 feet of thickness could be attributed to it. Above 

 this sandstone is whitish argillite, a soft rock, easily degraded, and fossiliferous. The dip of this 

 upper bed is very variable, dipping in every direction east and west, and occasionally vertical. 

 It appears to have suffered considerably by the talcose upheaves and by subsequent denudations, 

 the terraces which are found at the base of the range being covered with angular fragments 

 derived from the degradation of these strata. The fossils of these strata are described elsewhere 

 in this report. The total thickness of this upper bed is about 80 feet where observed. The 

 sandstones which lie beneath this are of two kinds, brown and red. The brown beds are soft 

 and easily decay ; the other bed is made of white quartz grains in a reddish paste ; this bed is 

 not fossiliferous, but at several points between the Mission Solidad and San Miguel, these two 

 bands of sandstone were separated by a calcareous stratum, whitish, and in places 15 feet thick, 

 with particles of comminuted shell, and casts of Dosinia alta, and ohliqua, and a small Venus. 

 Above both sandstones were found, near San Miguel, (south,) occasionally cropping out, Oslrea, 

 Hinnites, a,ni Palliiini ; but few specimens could be collected complete, owing to the brittle 



