60 
AGE OF THE SEDIMENTARY BEDS. 
observed as axial beds, here producing an anticlinal axis of trap and serpentine, and throwing 
the serpentine and sandrocks on each side. The beds in proximity to the volcanic rock were 
the serpentine and trap conglomerate, upon these the red and brown grits, and above all the 
soft calcareous and clay beds observed in the Santa Maria valley. The rocks in juxtaposition 
with the serpentine were stated to be very much hardened and metamorphosed. There is no 
distinct pass in this locality, but deep gorges, the present bed of the river, which winds its way 
tortuously around and across the ridges. The range is not a continued crested ridge but a 
series of smaller ridges 8 to 12 miles long, which have a direction somewhat more east and west 
than the direction of the main chain ; thus, while the trend of the range is north 46° west, 
that of the several links is about north 60° west, running their southern extremities into the 
inland valleys ; through one of these re-entering angles the pass is found. 
The age of the stratified sandstones has been already noticed in describing the Santa Margarita 
valley, in which they occupy a well marked basin position. 
■But what shall be said of the metamorphic limestone, found lying below the serpentine con¬ 
glomerate, and lying between it and trap, to which latter rock it has contributed considerably, 
by the filling up of the cavities? Were this layer met for the first time it would not have 
demanded attention, but it had been already met in San Jose valley, flanking the serpentine 
along the west of the valley, where it may be traced for 30 miles continuously. Inquiry from 
those living in the Salinas valley near hills, ascertained that it lay up the mountains on the 
east side ; it has been described as lining the San Juan valley on both its sides, and it is well 
known in the neighborhood of Monte' Diablo ; on the west side of G-avilan it is found 400 
feet thick, and in Alameda county at Oaklands, nearly opposite San Francisco, across the 
bay, a magnesian limestone has lately been found. Thus a bed of stratified blue limestone has 
been traced on both sides of San Jose valley, and, therefore, underlying it, also underlying 
San Juan ; found on the east side of the Salinas valley, and on the west of Santa Margarita. 
Further south on the Coast Range it has not been detected, but this may be owing to the fact 
that the upheaval has not been sufficiently powerful, since the green conglomerate is rarely 
elevated in those lower ranges so as to expose its whole thickness. 
Passing inland to the Sierra Nevada, a limestone bed is also found, as a primary rock, a 
crystalline carbonate, found in the Canada de las Uvas, lining both sides of the pass, found 
in round masses washed out of the Cajon pass, and also in every other pass of the Cordilleras, 
where it was looked for; it is there in contact with granitic rock, and should it chance to be coeval 
with the blue limestone of the Coast Range, its characters of resemblance are wholly gone; 
but what is the age of the latter ? is it silurian, carboniferous, or upper secondary ? In the 
absence of the exploration for fossils in the quarries in San Jose valley, or at Monte Diablo, it 
were idle to speculate; and knowing that in the territories north of this State carboniferous 
limestone does exist, one would be hardy who would deny this to be of palaeozoic age. 
A section of this range, obtained from the canon of the Santa Maria river, is given in figure 2, 
plate 2. Plate l T, figure 2, affords a section through the pass of San Luis Obispo, leading into 
San Luis valley, and the relative position of the chain is shown in plate 1, figure 2, and plate 5, 
figure 1. 
