BENICIA SANDSTONE—LITHOLOGICAL CHARACTERS—FOSSILS. 
151 
SECTION OF THE STRATA AT NAVY POINT, BENICIA. 
Feet. 
R " 1 
locality ; 
1. Sandstone, fine-grained and soft, with spherical masses of great hardness inclosed—only about 10 
feet exposed___-___ 10 
2. Sandstone, harder than No. 1, and highly charged with peroxide of iron.._... 15 
3. Sandstone, with layers of small pebbles and coarse grains of quartz. Some hard masses also 
seen. Ferruginous. Fossils and a shark’s tooth_______ 20 
4. Slaty sandstone in thin layers, hardened by the presence of a considerable portion of oxide of iron. 
Trend S. 75° E. ; N. 75° W . 6 
5. Slaty sandstone, similar to No. 4.........'___ 15 
6. Sandstone, fine-grained, soft, regularly bedded_________ 63 
7. Sandstone, soft, in beds separated by thin partings of shale, and traversed by thin seams of gyp¬ 
sum, generally in horizontal layers. The shales and the beds of soft sandstone are much 
stained by oxide of iron____________ 30 
8. Sandstones and shales, all soft and decomposing; some of the beds consist of fine-grained white 
sand. The general characters are the same as the previous beds. Thickness of this series, from 
No. 7 to the point of conglomerate, estimated to be 600 feet_____ 600 
9, h. Conglomerate of gravel and pebbles forming the end of the point----- 25 
10, g. Decomposed silicious sandstone traversed by nearly horizontal seams of gypsum, and divided 
in the centre by a thin parting of shale..... 30 
11, /. Thin layers of sand or sand and clay, forming a kind of shale___ 1^ 
^ 12, e. Decomposed sandstone, containing some hard masses, and traversed by seams of gypsum, 
: partly fibrous ___ 15 
| 13, d. Thin layers, finely stratified, like No. 11....... 1£ 
^ 14, c. Soft decomposed sandstone—----— ...- 16 
g 15, b. Soft decomposed sandstone stained by waving lines of peroxide of iron, looking like the grain 
of wood.—....... 6 
p* 16, a. A succession of beds of sandstone and thin partings of shale, all more or less discolored by 
* oxide of iron, and traversed by seams of gysum in nearly horizontal lines. Thickness about 
5 150 feet........... 150 
g These strata are all conformable, and the combined thickness is a little over one 
m thousand feet. The section commences at the low ground on the western side of 
* the point near a quarry, and extends along the beach, under the face of the bluff, 
g to a little cove, where the rocks are no longer exposed. The dip and general 
| appearance of the strata are shown in the appended section ; an enlarged view of a 
portion of the series is presented on the sheet of sections, Chapter XIII. This 
portion is that lying east of the conglomerate, and it is indicated in the descrip¬ 
tive section by letters which refer to the plate. It includes a thickness of about 
175 feet. 
The quarry was opened in the thickly-bedded sandstone, containing hard, rounded 
masses, which, when broken open, revealed a bluish nucleus similar in color to 
that of the rock at Yerba Buena and other localities near San Francisco. These 
hard masses seemed, at first, like concretions, but they probably originate in the 
same manner as the spheriods at Yerba Buena—by decomposition of angular blocks. 
When these nuclei are broken up, they are found to contain small dark-colored 
plates and fragments of an earthy character, but apparently the remains of lignites. 
In some of them, the carbonaceous material is quite apparent; and in the softer 
and more decayed parts of the rock, I found several specimens in which the organic 
structure of plants was well exhibited. The small black films in the sandstones 
of the bay of San Francisco, that have already been described, all lie in planes 
parallel with the stratification, and are similar to those in the hard masses of this 
and I consider them, in part, as ©f vegetable origin. The thickness of this stratum, 
