Slike strani
PDF
ePub

DISEASES OF SILK WORMS.

As yet there are no diseases in the cocooneries of California. The only pest is ants, which attack and destroy the worms, but they are readily avoided, by keeping the legs of the stands in water. But in order not to be led into French errors, which have bred disease, it may be well to mention the cause of its introduction in France.

Firstly: A system has been pursued there for some years, under the guide of science, of forcing the trees '' to give all their vital powers to the production of greater leafage." This is done by just such artificial substitution for the natural law of growth as is applied to grape culture. Pruning knives and close stripping of the leaves have wrought the mischief. So, likewise, depending solely on varieties which make greater weight of leaf, not sufficiently regarding the health and quality of the food nor the strength of silk it makes.

Secondly: Selecting eggs from the biggest cocoons only, year after year. The law is the same for all living organisms. The silk worms of France have lost their vigor—they can no longer stand a thunder storm—they cannot clear the silk they spin of the surplus silicious matter, which in delicate humanity cumbers the kidneys and is an obstacle to every function of the bodily organs. This is the cause of the "cutting" of modern silk fabrics, and the absence of the enduring silk dress goods of former times.

CHAPTER VI.

GEOLOGY.*

General Outlines of Topography—Geology of Coast Ranges — Monte Diablo Range—Coal Beds—Peninsula of San Francisco—North of San Francisco Bay—South of Monterey Bay -Southern End of Tulare Valley—Geology of the Sierra Nevada The Great Auriferous Belt—Southern portion of the Gold Field—Mariposa County—The Fremont Grant —Mining—Tuolumne County—Table Mountains - Fossil Remains—Calaveras CountyUnion Copper Mine -Gold Mining -Amador County—El Dorado County—Placer County Nevada County—Sierra County—Plumas County.

The main physical features of the State of California are so prominent, and arranged upon so grand a scale, that a general view of its topography is essential to a proper comprehension of its geology. The coast line stretches in a northwesterly direction from about the parallel of 32° 30', to that of 42° north latitude. It is but little broken up, the most marked indentation being the Golden Gate, the outlet of the bay of San Francisco. The State has a nearly uniform width, from east to west, of two hundred miles. A great central valley, having its longer axis in a direction northwest and southeast—that is, parallel with the general trend of the coast, is inclosed and bordered by the Sierra Nevada mountains on the east, and the Coast Range on the west. The northern end of the valley is formed by the junction of these two mountain ranges near Shasta City (latitude 40° 35'), and the southern by the union of the same, near Tejon Pass (latitude 35°). North and south of these two points it is solely for geological considerations that the line of demarcation, between the Sierra and Coast Ranges can be drawn; for, topographically, they are one and the same.

* In the preparation of this chapter the following authorities relative to the geology of California have been consulted, viz.: Reports of the State Geological Survey: Prof. J. D. Whitney; Pacific Railroad Reports; Geological Reconnaisance in California: W. P. Blake; Placers of the Middle Yuba: Prof. B. Silliman; De la Production des Metaux Precieui en Californie: P. Laur; and Proceedings of California Academy of Sciences. To the former of these, as being the only work based upon a systematic survey of the State, we desire particularly to acknowledge our indebtedness.

The crest of the Sierra, which is marked by a long and nearly straight line of culminating peaks, extends from Mount Shasta to the Tehatchaypah Pass, a distance of nearly five hundred miles.

The ascent from the great central valley of California to the summit of the Sierra is comparatively easy and gradual, but the eastern slope of the chain is bold and abrupt, and forms the western wall of that vast sterile tract of country included between the Rocky Mountains on the east and the Sierra Nevada on the west, in which are the great silver mines of Nevada.

The Coast Ranges are not so strongly marked by any one line of dominant peaks, but form a broad belt of mountains bordering the western part of the State, made up of minor ridges having a general parallelism of trend to each other and the coast; between which, particularly south of the bay of San Francisco, are included long and narrow valleys remarkable for their productiveness and salubrity.

The great central valley, which, with its bordering mountain chains, embraces the middle, larger, and by far the most important part of the State, is drained by the Sacramento and San Joaquin rivers. These are the main commercial arteries of California; furnishing, as they do, the means of rapid and cheap transportation from the coast to the interior, both north and south. The former rises in the neighborhood of Mount Shasta and flows south, receiving numerous tributaries from the east, fed by the melting snows of the Sierra—the latter runs in a general northerly direction, having its corresponding affluents from the east, and both uniting at a point about midway on the western side of the valley, just north of Monte Diablo, discharge their waters successively into Suisun, San Pablo and San Francisco bays, and from thence through the Golden Gate into the ocean. This succession of bays is the only break through the Coast Ranges that extends from the great central valley to the ocean.

Our geographical and geological knowledge of the extreme northern and southern portions of the State is very limited. Both are thinly settled, and from natural causes have not received as large a share of attention as the middle and great gold producing section.

Having thus given a general view of the mountain chains, valleys, and rivers, we now pass to the consideration of the geological structure of the former, and of those facts which bear upon the mineral wealth of this wonderfully rich and favored State—a subject that demands far more than the limited space at our disposal, but of which the most important facts and salient features hitherto ascertained are here given.

MONTE DIABLO RANGE.

Of the numerous minor mountain ranges which together make up the broad belt of elevations between the great central valley and the ocean, the one which has been most thoroughly studied, and furnished by far the greater part of the data upon which conclusions have been formed as to the geological age of the others, is the Monte Diablo range proper, extending from Suisun Bay on the north to Paso Robles, near Fort Tejon, on the south, a distance of over one hundred and fifty miles. To the consideration of the geology of this range, therefore, more space is devoted than to that of either of the others ; and, further, because in structure and material it is in a high degree similar to them, being constituted of strata of the same geological age, and rocks similar in their lithological characters. Its eastern border, along the central Valley, is well defined; but on its western side are numerous spurs jutting obliquely to the northwest, that form for comparatively short distances distinct local mountain ranges, but which are finally merged into the more continuous range known as the Monte Diablo, receiving its name from its most northern peak, which lies but little north of east from the city of San Francisco, about thirty miles distant.

This mountain, though not as high as others in the chain further south, being but 3,876 feet in elevation, nevertheless, from the comparatively isolated position in which it stands, and the extensive view to be obtained from its summit, is its most conspicuous peak. It is also especially important on account of the coal beds that occur on its northern flank, which are of vast economic value to the State, being the only extensive deposits of coal yet discovered within its limits.

The range, which attains an average elevation of perhaps three thousand feet, is marked by depressions occurring at rather short intervals, the most important of which is Livermore Pass, a short distance south of Monte Diablo, being the lowest (680 feet), and affording an easy route for a railroad connecting San Francisco with Sacramento —an important link in the future great continental thoroughfare. The mountain masses are almost wholly made up of cretaceous and tertiary strata, often extensively altered, and presenting instances of peculiar local metamorphism. The general trend of the range is northwest and southeast, but the rocks have almost every possible dip and strike. Eruptive rock is not a marked feature of the chain, but occurs at various points throughout its length.

Monte Diablo itself is made up of a central mass of metamorphic Cretaceous rocks covering an area of twenty square miles, surrounded and overlaid by unaltered Cretaceous strata, upon which rest conformably the Miocene and Pliocene divisions of the tertiary, the eocene being apparently wanting. In the examination of the metamorphic rocks of Monte Diablo, the passage of Cretaceous shales into jaspery rock, and of argillaceous sand-stones into serpentine, is shown to great perfection, and is especially interesting, as these form such a considerable part of the rocks found throughout the Coast Ranges, and as it has been the means of identifying the age of rocks in other localities in which fossils are wanting or sparingly occur.

MONTE DIABLO COAL BEDS.

The Monte Diablo coal beds are in the upper limit of the cretaceous, in a ridge on the northern flank of the mountain, and dip at an angle of from forty-five to twenty-six degrees to the north, the inclination gradually becoming less and less as their course is followed to the east and southeast, to the San Joaquin plains.

The principal mining center is at Somersville and Nortonville, (small towns separated by a narrow ridge,) about five miles distant from the San Joaquin river, and from eight to nine hundred feet above it. The mines at both places are connected with the river by railroads, which have been constructed for the cheap and rapid transportation of coal to a point of shipment by water, and are somewhat remarkable for the necessary high gradients and short curvatures employed. The workable beds are two in number, varying in width from thirty to fifty inches, and furnish a good article of bituminous, non-caking coal. The topography in this vicinity has permitted the mines to be opened by tunnels, and comparatively short inclined shafts. The total amount of coal shipped from them during the past year, 1867, is stated to have been 109,490 tons—38,168 tons being furnished by the Black Diamond Company's mines at Nortonville.

Within the past year developments of the same beds have been in progress upon the "Rancho de los Meganos," better known as the Marsh ranch, at a point six miles east from the mines above mentioned, just within the limits of the eastern foot-hills of Monte Diablo, and at an elevation of one hundred and thirty-five feet above the river. Here the beds are less inclined, and it is highly probable that fewer faults or dislocations will be found in working them in this vicinity than at Somersville, where their inclination is steeper and the disturbances have been greater. At this point, being at such a small elevation above the river, their exploitation involves the sinking of deep shafts, and the

« PrejšnjaNaprej »