the tertiary sandstones are represented as resting conformably upon the cretaceous.

In the San Ramon valley are evidences of very recent disturbances; fissures in the soil are said to exist which were formed during the earthquake which occurred in the month of June, 1861.

Near Martinez, and for some distance west, along the shores of Suisun Bay and the Straits of Carquinez, cretaceous strata are well exposed, consisting of sandstones and shales, the latter with intercalated deposits of argillaceous limestone, varying in thickness, sometimes attaining a width of three feet or more.

The upper limit of these strata is marked by the occurrence of sandstones resembling those accompanying the coal beds at Monte Diablo, which, though containing much carbonaceous matter, do not present indications of a regular coal bed. They are overlaid by the tertiary strata, resting conformably upon them, which form the mass of the Contra Costa hills. In the tertiary strata, near San Pablo, oil has been obtained by boring, though not in sufficient quantitity to be of any commercial value. North of San Pablo are low hills made up of horizontal post-pliocene strata resting uncomformably on the edges of the tertiary.

THE PENINSULA OF SAN FRANCISCO.

This peninsula is marked by a high mountain range extending from the Golden Gate southeast as far as the Bay of Monterey, its connection with the Gavilan, previously mentioned as a spur of the Monte Diablo Range, being broken by the valley of the Pajaro river, which has its lateral branches draining the interior valleys both north and south. It is much broken, and cannot properly be called, as it sometimes has been, the Santa Cruz Range, though in Santa Cruz county it attains its greatest elevation and broadest development near Mt. Bache, and other high peaks in its vicinity. An almost unbroken front of mountains is presented towards the ocean, a narrow strip of table land alone intervening. Along the western shore of the Bay of San Francisco, howis a considerable belt of level land which widens towards the south, and joins with the extension of that on the eastern side, forming the San José valley.

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The geology of the belt of elevated land between the San José valley, the Bay of San Francisco and the ocean, is very similar to that of the Contra Costa hills, though it is rendered more complicated by the intrusion of granitic rocks. It is composed of the same cretaceous and tertiary strata, containing rocks similar in lithological character to

those of Monte Diablo, which have already been mentioned. Fossils sparingly occur. A metamorphic belt extends from Redwood City to the southeast a distance of about forty miles, forming the eastern edge of the range and the summits of Mt. Bache, 3,780 feet in height, and of other high points. Limestone, in detached masses, occurs at several places throughout this belt; evidences of what was once, in all probability, a continuous limestone belt, are found at various places, from the summit of Black mountain, back of Mountain View, to as far south as the New Almaden mines, which lie in a ridge northwest of that formed by the metamorphic mass of Mounts Bache, Choual, and Umunhum. It is to be seen on Los Gatos creek, dipping to the northeast, and is less altered there than at other places where it is hard and compact, though not crystalline. To the west of the metamorphic belt above mentioned is a series of unaltered tertiary strata, forming a broad range of mountains extending northwest through Santa Cruz into San Mateo county, the culminating point of which is Mount Bielawski, 3,269 feet high. Southwest of this belt of tertiary, and stretching northwest, nearly to Pescadero creek, is a high range of granite hills, at places attaining an elevation of 2,900 feet, the relations of which to the adjoining strata have not been thoroughly investigated. A mass of gold bearing quartz is said to have been found in this range of granite hills, and to have yielded quite largely--no well defined veins, however, have been traced, and the deposits, when they occur, are not likely to prove of permanent value.

Beds of miocene tertiary extend along the coast from Santa Cruz to Spanishtown; these retain their original position along the shore, but are disturbed near the granite. The coast is also marked by the occurrence of terraces, indicating recent changes of level, which, though broken at intervals, are to be seen throughout the distance from Santa Cruz to Pescadero. No eruptive rock is known to occur on the peninsula north of San Mateo. The range becomes depressed as the Golden Gate is approached, and at the head of the peninsula we have a mass of comparatively low hills made up of highly broken and contorted metamorphic cretaceous strata, without any apparent regularity of strike and dip. The material of Telegraph, Russian and Rincon hills, sections of which have been well exposed by excavations involved in grading the streets of the city, is an argillaceous sandstone-in places highly altered and durable, but generally soft, and disintegrating rapidly on exposure to air and moisture. Jaspery rock occurs in the outskirts of the city, and has been employed to a considerable extent as a ballasting material for roads leading therefrom. A belt of serpen

tine extends from Fort Point, by Lone Mountain and Mission Dolores, to the Potrero. The peculiar silicious rock generally associated with ores of mercury occurs at various points, and in the vicinity of the Mission some cinnabar has been found. No building stone of value occurs in the immediate vicinity of San Francisco. On Yerba Buena Island, in the bay, one mile east of the city, the rocks are similar to those of Telegraph Hill, though a highly altered sandstone, having a trappean appearance is exposed on its eastern side in larger masses, or more heavily bedded than at the latter locality. This, to some extent, has been excavated and used for foundations of buildings in San Francisco, and is a good material for concrete intended for sub-aqueous structures; its extent, however, is very uncertain, and large quantities of softer material have to be removed in its excavation. A less metamorphosed sandstone, often streaked with thin veins of carbonate of lime, is quarried on Angel Island, north of the city.

The miocene tertiary is not represented in the vicinity of San Francisco, though in the low hills along the sea shore southwest of Merced Lake, strata belonging to the pliocene and post-pliocene epochs, which are unconformable with each other, are exposed. These also rest unconformably upon the metamorphic cretaceous.

By far the most interesting and important feature of the range under consideration, is the occurrence of the extensive deposits of cinnabar in the metamorphic cretaceous rocks at the New Almaden mines, a few miles southwest of San José, and lying in a ridge east of the main range, culminating in Mount Bache, the highest points of which are about 1,700 feet above tide water. The three mines-the New Almaden, Enriquita, and Guadalupe-are in line extending over a distance of about five miles; the former is by far the most productive. The cinnabar occurs in altered slates, inclosed by extensive masses of serpentine. The ore is very irregularly distributed, though the metal bearing portions seem confined to limited areas dipping with the strata. This is but one of the numerous localities throughout the Coast Ranges where cinnabar is mined, but thus far is the only one that has been worked with very great and continued profit to its owners.

On the western side of the island called Red Rock, which rises abruptly from the waters of the bay, about eight miles north of San Francisco, and attains a height of about 250 feet, there occurs a dèposit of oxide of manganese (pyrolusite). This island is almost entirely composed of cretaceous jaspery shales. The ore is found, sometimes in quite large masses, irregularly distributed throughout a belt over one hundred feet in width, extending northwest and southeast across

the island, a distance of between six and seven hundred feet. It is of excellent quality, containing a high percentage of binoxide, and is remarkably free from iron, lime, or other materials for which chlorine gas has an affinity. The ore is accompanied by a black, flinty ganguestone, which is likely to be mistaken by the inexperienced eye for it, but which is of very much lower specific gravity, and is therefore easily sorted. Over two hundred tons, containing by analysis from carefully averaged samples over seventy per cent. of binoxide, have been shipped from this locality to New York, and sold for less than enough to pay freight and commissions. Although enormous amounts of bleaching powder, or chloride of lime, are consumed, nearly the whole of it is imported from England, its extensive manufacture having been but recently commenced in the United States. The demand for it in New York city is therefore exceedingly limited. The price of oxide of manganese in the English market during the past few years has ranged so low-extensive deposits having been discovered in Spain, from whence that market is supplied, as to preclude the probability of the pecuniary success of its being mined here to any considerable extent. The actual cost of its delivery at Liverpool will probably exceed its value in that market, or at any rate equal it.

The rapid introduction of the chlorination process in California, for the extraction of fine gold from the auriferous sulphurets, will create a limited home demand for the article. As an agent for generating chlorine for bleaching purposes, the paper manufacturing companies would probably find a considerable saving to result from its use. In the method at present adopted by them-the employment of bleaching powder-the lime merely serves as a vehicle of transportation for the chlorine, which has already been generated by means of oxide of manganese. Other deposits of pyrolusite occur in the metamorphic cretaceous rocks, but they are apparently of very limited extent, and not likely to prove valuable.

NORTH OF THE BAY OF SAN FRANCISCO.

The valleys included between the Coast Ranges north of the Bay of San Francisco, though numerous, are generally smaller and narrower than those to the south of it. The mountain ranges are but a continuation of those already described, and are made up of rocks of the same general character-silicious and jaspery rocks predominating, and serpentine occurring in enormous masses, though volcanic rocks and materials play a much more important part than in the ranges south of Suisun bay.

Tamalpais, a conspicuous mountain on the north side of the depression which forms the Golden Gate, rises quite abruptly to an elevation of 2,597 feet. Its summits, of which there are three, consist of metamorphic sandstone, in some places marked by quartz veins having a banded structure. Heavy masses of serpentine occur on its western and northern slope. A ridge of this material, nearly 2,000 feet high, extends several miles to the northwest. A short distance west of the town of San Rafael, is a mass of trachyte extending some distance east and west.

Three quarters of a mile southwest of Petaluma, a belt or dyke of compact basalt occurs. In places it has a columnar structure, and is about two hundred yards in width. It has been used to some extent as a building material at Petaluma; its hardness, and the difficulty of obtaining stones of large size, render it undesirable for that purpose; but it makes a durable material for ballasting roads, or a concrete for submarine construction, this being the most accessible point to the city of San Francisco, where such material can be obtained in large quantities. Eruptive rocks also occur at points between Petaluma and San Rafael, but not as favorably situated for shipment as the basalt near Rudesill's Landing.

Between Tomales bay and Petaluma is a line of marked depression. In the vicinity of Tomales, the miocene tertiary, undisturbed and resting conformably upon the cretaceous, is represented. The belt of granite, which occurs on the west side of the peninsula of San Francisco, appears at the extremity of Tomales point; at Punta de los Reyes, which is wholly composed of it, and at Bodega Head, farther north. Limestone is associated with granite and mica slates at the head of Tomales bay, and it is probably the continuation of the belt which traverses Santa Cruz and San Mateo counties.

Mount St. Helena, 4,343 feet high, at the head of Napa valley, is, with the single exception of Mt. Hamilton, the highest summit between San Carlos to the south and the higher regions to the north. This mountain seems to have been the source of the volcanic materials, which are spread over a large area of country to the east and southeast of it. A belt of eruptive rock extends from the west side of Clear Lake through to Suisun Bay. Hot springs, which have an extended reputation for their curative qualities, are numerous, especially in the vicinity of St. Helena, and Clear Lake. North of St. Helena are several localities where cinnabar has been found and mined to some extent.

Perhaps the most important development is in Pope Valley, three miles northeast of Mt. St. Helena. The rock, an imperfect serpentine,