152 
GEOLOGY. 
or series of layers, of compact sandstone, containing the hard nuclei, was not ascertained, and 
at this time I find it difficult to assert with certainty whether it forms a part of the series 
exposed along the beach. It is recorded as a part of the section in my note-hook, hut it is pos¬ 
sible that the strata were only seen at the quarry, which is several rods distant from the exposed 
strata along the beach. I have, however, little doubt of the continuity of the strata, and that 
they are conformable. This is an important point; for the similarity of the lithological charac¬ 
ters of the sandstone to that of San Francisco is, under the circumstances, good evidence of the 
synchronism of the strata at the two places. In other respects, the strata, as exposed in the 
section, have little resemblance to those around San Francisco. There is no doubt of the presence 
of the equivalents of the San Francisco sandstone in the vicinity of Benicia, for a similar rock 
is quarried in quantities and sent down to he used in the construction of buildings. Many of 
the stones, when dressed and rubbed down, show a central portion of a dark color identical in 
its characters with the rock from the quarries of the hay. 
The thin seams of gypsum, which occur so abundantly in the strata, are not found in layers 
parallel with the beds ; they are nearly horizontal or curved downwards, thus showing that 
they are the result of infiltration from above. Such is also the origin of the undulating layers 
of oxide of iron, which in many of the beds are so numerous and parallel, and at the same time 
so much bent and plicated, that it at first seems as if the bed was formed of compressed and 
crumpled shales. The uniform width of the stratum, and the parallelism with the adjoining 
strata, show, however, that the appearances have not been produced by violence. Fine exam¬ 
ples of the deposition of oxide of iron in layers and curved lines were afterwards seen in the 
horizontal strata along Ocoya or Pose creek. 
The fossils which were observed were very few and imperfect; with the exception of a shark’s 
tooth, they are mere, broken casts, all the shells being removed, and the forms left in a matrix of 
sand and peroxide of iron. As near as can he determined, the genera Trochus and Turritella 
are represented. The shark’s tooth is well preserved, and, according to Professor Agassiz, 
represents a species of Lamna allied to L. elegans, Agass., which is found in the Calcaire 
grossier in the environs of Paris, and in the London clay at Sheppy. The description, by Pro¬ 
fessor Agassiz, of the new species, under the name of L. ornata, will be found in Article I of 
the Appendix. These fossils are regarded as sufficient to establish the Tertiary age of the 
strata from which they were taken. 
It will be seen from the observations recorded in the Itinerary that the strata of Benicia are 
prolonged towards the south and southeast, on the opposite side of the straits. A conglomerate 
and similar sandstone to that of Benicia was found south of Mount Diablo, at Livermore’s Pass. 
The strata are believed to have a wide extent in that direction, and to form the greater part of 
the Contra Costa or Central range. The sandstone and shales of San Francisco have a similar 
extension towards the south, and it is probable that the stratified rocks at the New Almaden 
cinnabar mine are of the same age. These strata much resemble those of San Francisco,,and 
are similarly associated with serpentine. A great body of sandstone is found still further south, 
flanking the San Juan mountains, on the side towards the valley of the Salinas, and I am 
inclined to include this in the same group. At the last-mentioned point it shows a great thick¬ 
ness, and crops out in great, massive beds, many feet in thickness. The strata dip away from 
the axis of the range at an angle of about forty degrees. 
The prolongation of this group of strata is not, however, confined to the southern ranges of 
the Coast Mountains. The rocks are found developed in the mountains north of the Golden 
