180 
GEOLOGY. 
MONTEREY. 
Point Pinos, the northern termination of the Santa Lucia range of the Coast Mountains, is 
formed of a gray, porphyritic granite, and by its hardness and resistance to the sea, forms a 
bulwark or breakwater for the hay. The Tertiary formations adjoin this granite on the inner 
side of the point, and extend for many miles inland towards the southeast. They are of 
different colors, generally very light, and are composed of fine materials. Several quarries have 
been opened in the strata near the town, and the rock is used for buildings and walls. The 
strata are composed of argillaceous and fine, silicious materials, so fine that the grains are not 
easily visible. The rock is very light and porous, and when the blocks are freshly broken out 
from the quarry they can be easily hewn into shape by an axe, being free from coarse grit or 
gravel. The colors are chiefly light-yellow, or buff of various shades, and a fawn-color or drab; 
some of the beds are dark-greenish black or olive-brown. A light-yellow or buff, similar to 
that of lithographic stone or Bath brick, is, however, the prevailing tint. In density the rock 
is somewhat similar to Bath brick or the biscuit-ware of the potter, and, like both, it rapidly 
absorbs water when dry. The large Court-house, built by Walter Colton, and the church, 
erected in 1*794, are constructed of this stone, and the sharp edges and angles which are retained 
by the blocks in the walls of the latter show that the material has great durability in that 
climate, and is well adapted to purposes of construction. 
Some of the darker strata, though indurated and apparently without any volatile constituent, 
are bituminous, and give off an empyreumatic odor when heated before the blow-pipe flame. It 
is most probable that this bitumen is of animal origin, and its presence would not be suspected 
on examination by the eye merely. 
These light, porous rocks form the principal part of the hills in the vicinity of the town, and 
extend towards the Bay of San Carlos and the Yalley of the Carmello. The Mission of San 
Carlos, near the mouth of the Carmello, is built of them. These strata are probably near the 
base of the formation at Monterey, and rest directly upon the granite. No coarse materials 
were observed, but at the Bay of San Carlos there is a coarse conglomerate in thick beds, 
which appears to adjoin the granite and may underlie the softer and finer strata, but they were 
not seen in proximity, and it is doubtful whether the conglomerate is not much more recent in 
its origin. 
Higher up in the series of strata, and at the summits of some of the hills, we find a most 
remarkable series of chalk-like beds, which consist, in great part, of the remains of silicious 
infusoria. The strata attain a great thickness, and are probably the most extensive and 
interesting deposit of marine microscopic organisms hitherto discovered. 1 
The principal outcrop, so far as yet known, is visible from Monterey and the anchorage of the 
bay, and appears as a white spot in the side of a hill about two miles from the centre of the 
town. This hill attains an elevation of over 300 feet above the bay, 2 and is separated from it 
by a broad, sandy plain and a belt of sand-hills along the beach. Groves of oak are found 
around the base of the hill, but towards its top it is covered with a dense growth of chamizal, 
(shrubbery,) through which the outcrop of white earth can be seen from a distance. The 
principal outcrop is an exposure 100 feet in length by from 15 to 40 in width, and it is seen to 
1 A notice of this deposit was communicated to the Academy of Natural Sciences of Philadelphia, in April, 1855.—See 
Proceedings. It was also described at the meeting of the American Association, in Providence, 1855. 
2 In the notice of this deposit the elevation of the hill was stated as 500 or 600 feet. I have reason to conclude that this 
estimate was two high. 
