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removal of considerable quantities of water by pumping-a difficulty which substantially constructed works and adequate machinery will overcome. The limited extent of our coal field renders this new development especially important, and it is probable that before long numerous collieries will be established east of the principal mines, which have heretofore furnished nearly all the coal shipped from the Monte Diablo beds.

In connection with the coal on the Marsh ranch, an extensive bed of superior clay occurs. This furnishes the material for the pottery established during the past year, at Antioch, on the San Joaquin river, ten miles distant. The success of the enterprise has been even greater than was anticipated, and these works are now producing large quantities of earthenware, as good, if not better, than that imported from the Eastern States, and at a lower price. Fire-brick have also been made from this clay, which, it is claimed, are equal in quality to the best "Stourbridge" brick.

In this connection it will not be out of place to suggest to the companies interested at Somersville and Nortonville, a combination of their interests, and the driving of a tunnel starting from the plains bordering the hills, and between them and the Sacramento river, at as low a level as possible, and running so as to cut the beds at right angles to their strike. Such a tunnel would probably not exceed three miles in length, would afford perfect drainage and ventilation for the mines, and would materially reduce the cost of their development and the extraction of coal. It should be wide enough for a double track or tramway. The expense of its maintenance would probably not surpass, if it should equal, that of two railroads with high grades and short curves, while the cost of transportation would be considerably diminished. Another most important consideration is the opportunity that such a tunnel would afford for working the mines to a greater depth than could otherwise be attained. The soft and friable nature of the unaltered rocks which overlie the coal beds would render the work comparatively inexpensive and easy of execution.

Analyses of the Monte Diablo coal, made quite early in the history of the development of the mines, show it to contain a remarkably small percentage of ash and sulphur, but a large amount of water. A marked improvement in the quality of the coal since the mines have been opened to a greater depth, and these analyses were made, is acknowledged.*

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An analysis of Monte Diablo coal, from the Pittsburg mine, made in January, 1867, by W. P. Blake, shows the following result: Water, 3.28; bituminous substances, 47.05; fixed carbon, 44.90; ash, 4.71; no sulphur.

Both copper (chalcopyrite) and quicksilver (cinnabar) ores have been found in the metamorphic cretaceous rocks of Monte Diablo, but neither promises to be of future importance, as they occur in very irregular deposits of limited extent. Northwest, and in the vicinity of Monte Diablo, are extensive deposits of travertine or calcareous tufa, consisting of a very pure carbonate of lime, deposited from water of hot springs containing lime in solution, which undoubtedly existed at one time at the localities where they occur. The present expense of fuel and transportation prevents these deposits from being quarried and burned for lime.

SOUTH OF MONTE DIABLO.

South of Monte Diablo, a depression in the tertiary hills, and extensive denudation, owing to the soft and unaltered character of the sandstone, form Livermore Pass. The strata on the east side dip to the northeast, and on the west to the southwest. Within a short distance south of this pass deposits of coal, known as the "Corral Hollow" mines, occur, and evidences of the approach to another metamorphic center are to be seen. The bed or beds attain a greater thickness than at Monte Diablo, but are more disturbed, and show numerous faults or dislocations. They stand at a high angle, and dip in opposite directions within a short distance. Attempts have been made to open these mines, but they have thus far proved unsuccessful. The coal here is at about the same elevation above tidewater as at the Monte Diablo mines.

From this point, going south to Pacheco Pass, a distance of fifty miles, the range rapidly rises, becomes broader and very rough, having many elevated points along it, the highest being Mount Hamilton, nearly east of San José, 4,443 feet high. The range then decreases in height to Pacheco's Pass, the loftiest point of which is 1,470 feet. Between Livermore and Pacheco passes the San Pablo hills on the east side of the bay, so prominently seen from San Francisco, become merged into the main Monte Diablo range.

South of Corral Hollow, on the eastern side, in the numerous cañons opening into the San Joaquin valley, the structure of the range is well shown. It consists of a center of metamorphic cretaceous rocks, flanked by an enormous thickness of unaltered cretaceous strata. The latter consist of sandstones, with interstratified shales. A coarse conglomerate, the boulders in which are of metamorphic rock differing from that composing the main mass of the mountains, occurs on the outer margin of the hills towards the San Joaquin plain.

These unaltered cretaceous and tertiary strata flank the entire range

on the eastern side, as far north as its junction with the Sierra Nevada. The absence of the tertiary is marked by the precipitous nature of the range where it joins the plains, as opposed to the low rolling hills where the tertiary overlies the cretaceous.

Along the eastern flank, the tertiary, as far as known, rests conformably upon the cretaceous, as at Monte Diablo. The metamorphic rocks in this vicinity have the same general characters, being marked by jaspers, serpentine, and occasionally mica slate. Their limits are well indicated by the growth of forest trees, which is very meager upon the hills made up of unaltered strata, they being generally very dry

and barren.

At the mouth of Lone Tree Cañon is an ancient terrace underlaid by cretaceous shales, and covered with deposits of gravel. The metamorphic center of this range extends south of San Carlos mountain, which is nearly the culminating point, and in the broadest part of the range-its height above tide water being 4,443 feet.

The summit of Pacheco's Peak, a little south of east from the town of Gilroy, as well as those of other and higher peaks, in a line crossing the range obliquely to the southeast, are of trachyte. This is the first known occurrence of eruptive rock in the main Monte Diablo Range south of Suisun bay. To the south, the tertiary belt on the eastern side appears to widen, and at a point a few miles east of the New Idria mine it is believed that the Eocene epoch of that age may be represented—which is notable as being, perhaps, the only locality of Eocene yet discovered in the State.

Cinnabar is found at various points in a line extending from San Carlos to New Idria, a distance of three miles. The deposits have been developed by the New Idria Quicksilver Mining Company, and have yielded, and are now producing, a considerable amount of metal. The mines are just within the eastern limits of the metamorphic cretaceous. The rocks are sandstones and slates, in various stages of metamorphism. The ore, which is largely intermixed with iron pyrites, occurs in these rocks in very irregular deposits.

In Monterey county, on Clear creek, an eastern branch of the San Benito-which, as is characteristic of the streams throughout the Coast Ranges, flows for some distance nearly in the direction of the stratification, then turning abruptly to the west, breaks through the hills in a narrow gorge, and joins the San Benito at a point about forty miles south of San Juan-are other deposits of cinnabar extending, over a distance of two or three miles to Picacho Peak, some ten or twelve miles west of San Carlos mountain. This line is marked by very bold and

massive outcrops of the peculiar silicious rock, known throughout the Coast Ranges as "quicksilver rock." It is often highly discolored, by decomposition of iron pyrites probably, and traversed by veins of pure white quartz, affording most beautiful specimens of chalcedony, often with most exquisite drusy surfaces of minute quartz crystals. This line of outcrops, resembling fortifications, as seen from a distance, crowning the summits of the hills, from its durable character has withstood the action which has disintegrated and removed the softer magnesian rocks which appear to inclose it, bringing them out into bold relief. It is understood that developments are now in progress, with, however, the doubtful prospect that must ever attend the search for ore which occurs in such uncertain and irregular deposits as cinnabar. Should they prove successful, the locality is in every respect favorable for its economical reduction in close proximity to the mines, wood and water being abundant, conditions that are not as favorable at the New Idria mines farther east.

The San Benito valley is long, narrow, and nearly straight, and separates the Gavilan from the main Monte Diablo Range, for a distance of about seventy miles. The stream of the same name has its main sources in their point of union. The rocks occurring along its course are generally metamorphic and largely magnesian; frequent enormous land slides in the hills bordering the eastern side of the valley are seen to have taken place quite recently. During the dry season, the stream, which is small, appears only at intervals of ten or twelve miles, and the water is strongly alkaline to the taste. Near its sources it flows a constant and steady stream of good water.

Not far from the quicksilver deposits just mentioned, and the San Benito river, large masses of chromic iron are found. This ore of chromium also occurs between New Idria and San Carlos, in enormous masses, and, in fact, led to the discovery of the quicksilver mines. is not unlikely that the San Benito mines are but the extension of the New Idria deposits farther east.

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On the Arroyo Joaquin Soto, an eastern branch of the San Benito, further north, are enormous deposits of post-tertiary gravel, in some places greatly disturbed, even dipping vertically-a fact which is very interesting, as an illustration of how recent and extensive disturbances. have taken place in the Coast Ranges. Terraces, in one instance five in number, are found in this cañon, which Prof. Whitney remarks in his report, seem to have been formed by successive elevations rather than by gradual erosion at the mouth of the valley.

The tertiary is more extensively developed on the western than on

the eastern side of the Monte Diablo Range, towards the north. The hills bordering the San José valley on the east belong to this period, and are from one thousand to twelve hundred feet in elevation. The rocks are highly altered in places. A tertiary ridge extends to the northwest, separating San José and Calaveras valleys.

THE CONTRA COSTA HILLS.

The Contra Costa hills, so marked a feature of the scenery to be observed from San Francisco, are separated from the main Monte Diablo Range, first by the San Ramon, and farther south by Amador valley, and extend from the Straits of Carquinez to the southeast about fifty miles, joining the main range in the vicinity of Mount Hamilton. They are made up principally of unaltered cretaceous and tertiary strata, though a broad belt of the latter forms the mass of the hills. A belt of highly metamorphic rocks, rarely over two miles in width, extends from San Pablo to the southeast, a distance of thirty-five miles, forming the summits of the highest peaks, 1,500 to 2,000 feet in elevation, in the vicinity of the pass leading from Oakland to Lafayette. Near Redwood Peak this belt branches, one fork continuing to the southeast, finally unites with the central metamorphic mass of Mount Hamilton, the other skirting the western slope towards Alameda Cañon, where but traces of metamorphism are to be seen.

The rocks are similar in lithological character to those of Monte Diablo, and when metamorphosed, to those of known cretaceous strata near Martinez, on Suisun Bay, which consist largely of jaspery slates, and are marked by the occurrence of serpentine and the silicious ferruginous rock which occurs throughout the Coast Ranges in connection with cinnabar. Chromic iron also occurs in considerable quantity east of the town of San Antonio; and although it has been mined to some extent, its present distance from a market would preclude the possibility of its being profitably worked.

Unmistakably eruptive rock occurs at points throughout this metamorphic belt, though it is often difficult to distinguish between eruptive and metamorphic, on account of the high degree of alteration which both have undergone.

There is but little regularity of strike and dip of the strata forming the Contra Costa hills; in their northern part they form a well defined synclinal axis, as is shown by the section given on page 14 of the report on Geology of California, and taken between a point on the road from Martinez to Pacheco, and the Cañada del Hambré, in which

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