48 
IGNEOUS EOCK—GOLD PLACEES—FOSSILS OF THE SANDSTONE. 
Sequoia flourish, down even 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 1854-’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 places 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 
way 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 obliqua , and a small Venus. 
Above both sandstones were found, near San Miguel, (south,) occasionally cropping out, Ostrea, 
Hinnites, and Pallium; but few specimens could be collected complete, owing to the brittle 
