along the west side of the river, rising about a hundred feet or more. It is about 40 feet thick. Underneath are washed gravels, once the bed of the Sacramento River, and down which the lava flowed. The basalt being harder than the bedrock, the river cut its bed by its side, frequently crossing it and reducing it to disconnected patches on the sides of the valley. A little north of Delta the lava rises 200 feet above the river, and is nearly 100 feet thick.

Slate, together with sandstones, forms the country rock for 2 miles up Dog Creek; strike north and south, dip 30° east. Above these are quartz porphyries, dioritic rocks, and porphyritic conglomerates or tufas, probably eruptive. There are also many dikes of a beautiful diorite porphyrite. The latter rock occurs as dikes and bunches traversing the country everywhere in the vicinity of the Dog Creek Mines, 6 miles from Delta. At the Dog Creek Mines slate appears again and forms the rock toward the divide. It is cut by dikes of a greenish, slightly porphyritic rock and diorite porphyrite. At the contact of the dikes with slate are the goldbearing quartz veins. The greater portion of the gold is found in iron sulphurets. Very little development was shown here at the time of my visit; however, the veins do not appear to have a great deal of regularity, often pinching out or being cut off by cross dikes.

Slates are the only rocks exposed along the Sacramento River between Delta and Slate Creek. The dip and strike are exceedingly various. A large area of serpentine begins north of Slate Creek and forms the mountains northward between Shasta and Trinity Counties. It is met first about a mile and a half west of the road, in the form of more or less small detached masses intruded in the slates. Good exposures cannot be seen, on account of the great amount of soil covering the hills. In the serpentine are dikes of white granular mineral, probably malacolite. The serpentine extends west to the county line, the upper waters of Slate Creek heading in it. It is generally massive and hard, with some talcose layers running through it.

In years past considerable placer mining has been done on Tom Neal Mountain. The source of the gold has never been discovered, but it is quite likely that it has been derived from the talcose strata in the serpentine, which in some places prospects a little. The gold has a black coating, which is proof of its origin in the serpentine. Traces of silver have also been found. At one spot a tunnel was run, in an attempt to find the veins. It cut a diorite dike and serpentine schist, which is full of large cubical pyrite crystals. Other dikes of malacolite were also seen. here running north and south. South of Boulder Creek another dike of this rock was found. It contains scaly molybdenite disseminated through it, forming a very pretty rock. Very beautiful specimens of foliated talc were found in the serpentine on Boulder Creek. The talc layers often contain pseudomorphs of calcite after pyrite. Octahedrons of magnetite are also numerous in some of the tale schists. Actinolite is also found here. These crystals are not found in the massive serpentinoid rocks. Chromite occurs in spots, but not in sufficient amount to work. North of Little Slate Creek the serpentine approaches nearer the Sacramento River, and at Portuguese Flat it appears by the road. It continues to crop along the west side of the river as far as Southern's. It is generally bordered by altered diorites or green schists. The diorite forms high mountains east of the river. The mountains formed of diorite are more heavily timbered than those of serpentine, and the serpen

tine supports a better growth than the slates. The diorite extends a mile up Hazel Creek, and is there replaced by slates, which strike a little east of north, dip 50° to 60° east. The slates, together with much metamorphic rock like that on the McCloud, extend eastward to the head of the creek. Placer mining has been carried on for many years along this creek, but no veins have been found, though quartz is abundant.

Bunches of very coarse hornblendic rock are scattered through the serpentine, and in places it becomes gradually finer, blending into the serpentine. Although a large part of the serpentine of the State has been derived from pyroxene and olivine, yet I believe that this body, forming the mountains west of the Sacramento, and extending into Trinity County, have resulted chiefly from the alteration of hornblendes with some feldspar and olivine. Chromite is mined in places along the west side of the Sacramento River, and occurs abundantly in the washed gravels in the valley. The lava table-land continues along the river, chiefly on the west side, and while it decays to form a very fertile soil, yet makes an exceedingly rough road. North of Southern's the serpentine retreats to the northwest, and syenitic gneiss takes its place along the river. Five miles north of Southern's this strikes east and west, and dips at a high angle to the south. Near this point the river rises rapidly, and from there to its source flows on the lava which fills its ancient channel, instead of cutting through it. The lava gradually widens toward the north, and only in places is the bedrock exposed near the river. A fine view of the Crags is to be had from the mouth of Castle Creek. The creek is full of a great variety of granitoid and serpentine bowlders. Serpentine is found in places less than a mile up the creek. Its extent westward is about 7 miles, when it is succeeded by slate to the top of the divide. The slate strikes a little north of west, dip 30° north. The serpentine shows much variation, and has associated with it coarse and fine diorites. The serpentine extends many miles northwest into Siskiyou County.

The granitic rocks of Castle Crags are on the boundary between Shasta and Siskiyou Counties. They consist of jagged pinnacles, presenting the appearance of having been shattered vertically. The rock varies greatly in texture and composition; from that which is fine grained with more hornblende than mica and little quartz, to coarse porphyritic varieties with pink orthoclase in large finely formed crystals, and much biotite. In another direction it approaches quartz feldspar porphyry, having but little mica or hornblende. The peaks approach within a mile of the river.

At the Washington Mine the dikes are numerous, and vary from a dark, fine-grained variety with large porphyritic crystals of feldspar, to those with an almost granitic structure. The Niagara is much higher up the hill, but is in a similar formation, the rock being porphyry of different kinds. Long crosscut tunnels show the country rock very well. Four veins have been worked. The main Niagara vein, as well as the others, runs east and west, parallel to rather irregular dikes. The main veins dip to the south; one of the others to the north. In the lowest tunnel no vein appears. The character of the walls in the deepest workings is not distinguishable from those in the tunnel, 200 feet above where the vein is prominent; sometimes swelling to 10 feet, at others pinching to a seam of crushed porphyry. Bunches of slate crushed to black shining masses are inclosed in the porphyry. These are very

irregular, and wherever they encroach on the vein it loses its gold to a great extent. The bunches of slate are sometimes very small, but at the lower tunnel near the entrance is a mass several hundred feet thick. The walls of the northern vein are somewhat different from each other: The north wall is a felsite, the southern a coarse diorite porphyrite.

The summit of the divide between the Deadwood Mines and the Niagara Mine has an elevation of 4,300 feet. The rock is argillitic, but a little distance down the western side of the mountain occur dikes of porphyry, and granite. The granite at Deadwood seems to be the northern extremity of the granitic mass of the Trinity Mountains. The porphyry dikes are undoubtedly offshoots.

The mines of Deadwood are partly in porphyry and partly in granite. The granite lies mainly to the west of the town, where it outcrops for some distance along the road. Down the mountain argillitic rocks again appear, and strike east and west; dip north.

Near the base of the grade which leads up to Bully Choop the rock is a hornblende schist, changing to talcose schist; strike north and south, dip a varying angle to the west. About 5 miles up the grade is a dike of porphyritic diorite. The rock becomes more quartzose, showing many varieties of a talcose quartz schist, or sericitic schist. The latter are often of a shining white appearance. A mile east of the divide are dikes of diorite porphyrite running north and south. The schists assume a direction nearly east and west, and dip to the north, often at a small angle. The rock is quite uniform to the southern base of Bully Choop peak, where it strikes north 60° to 70° west, dip 65° northeast. The schists become more crystalline as the mountain is approached, turning to a hornblende schist, which in places becomes a pseudo-porphyritic hornblende gneiss. The main peak of the mountain consists of finegrained serpentine, with considerable coarse hornblende and feldspar rocks. The serpentine is often somewhat schistose, especially on its borders. There is an abrupt transition from the hornblende schist to the serpentine. The latter formation is 1 mile wide from north to south, and 3 miles from east to west, lying about equally on both sides of the divide. The serpentine is succeeded on the north by thin-bedded micaceous hornblende gneiss, rich in the dark minerals. This is followed by fine-grained rocks formed of quartz and feldspar, and in the course of several hundred feet there is an abrupt transition to a coarse hornblende granite, often slightly gneissoid. One dike of granite extends a little way into the schists. The contact runs parallel to the bedding of the schists, both in the case of the granite and of the serpentine. The granite extends north to Mount Bally, west 8 or 10 miles into Trinity County, and east nearly to Ono. A contact of the schist with the serpentine a half mile down the mountain shows that their boundaries are irregular, and small bodies of schist appear in the serpentine. Near the divide, a half mile south of the serpentine, are two bodies of white crystalline limestone. The limestone is reported to extend, though not continuously, 2 miles eastward, while another outcrop lies west of the divide. The schists on the north of the serpentine dip south 70° to 80°, while those on the south dip north.

This mining district contains veins conformable with the hornblendic and quartzose schists. They extend from some distance west of the divide in Trinity County, over the southern shoulder of Bully Choop, where the main development has been, to the Sunny Hill Mines, near

Bully Choop Mt.

Serpentine

the base of the mountain. The ore is characteristically gold-bearing iron and copper sulphurets, with some free gold. Much of it is quite base, carrying arsenic and iron in addition to copper. The ore belt has a width of about half a mile. Within this distance are a number of veins which occasionally show a thickness of 20 feet. The quartz is a bluish white variety. The walls are simply the country rock. Dikes of porphyrites were met in the tunnels, but they seem to have no relation to the ore deposits. Bunches of serpentine and granitic porphyry outcrop on the side of the mountain above the old mill. Extensive works were once carried on here, but it seems that they were unsuccessful, not from the lack of gold-bearing quartz, but from the inability to save the gold. With proper manipulation of the ores, this ought to become an important mining district. The height of the mines is 5,200 feet. They are reached by a grade 14 miles long, beginning near Watson's store.

Metamorphic
Igo.

Quaternary.

Granite.

Chanchelulla Mountain, southwest of Bully Choop, and rising nearly as high as that mountain, consists largely of quartzose and talcose schists. (Fig. 5 is a section east from Bully Choop through Horsetown.)

The shales of the Horsetown beds are well exposed in the creek beds about Ono. The noted fossiliferous localities lie between 1 and 2 miles below the town, on the Cottonwood and its branches. The granite appears about a mile west of Ono, and extends in a northeasterly direction, appearing 3 miles away on the road to Igo. The Horsetown beds terminate in coarse conglomerates resting on the Metamorphic Series and granite. This boundary follows an irregular line from Watson's store northeasterly, passing a little west of Ono and near Igo. More or less gold is found in these basal conglomerates. Many of the bowlders resemble silicious conglomerates in French Gulch. Sandstone is the chief rock seen along the road from Igo to Ono. It dips only 15° to 20°. Igo is situated at the western extremity of the modern gravels, which extend toward the Sacramento River in very even, gradually sloping ridges.

At Piety Hill extensive hydraulic mining has been carried on, and large amounts of gravel still remain to be worked.

The rocks exposed for 1 miles below Igo

belong to the Auriferous Series, and consist of quartzose argillites and some slate; strike nearly east and west, dip north. These are followed by diorite, or a feldspar hornblende rock, similar to that west of Muletown. Two and a half miles west of Igo granite succeeds this diorite. The South Fork Silver Mining District lies but 3 miles west of Igo. The veins cover a stretch of country 4 miles in diameter, and are situated wholly in the granite, or, perhaps, more accurately speaking, in the diorite, except those on the east, which lie at the contact of the granite with hornblende or argillitic schists. Near the contact the granite is greatly decomposed, and this portion also carries silver veins. One vein occurs in the schists outside of the granite. The veins on the eastern side run a little east of north, dip east, while those in the granite as a general thing run north 45 east. Those near the contact are, perhaps, the best defined. These also carry more silver and less gold, together with galena, zinc-blende, and copper. Those in the granite may or may not have gouge seams. Some veins are almost pure galena, carrying some silver. In others there is galena and iron pyrites rich in gold; there is no free gold. In still others there are both galena and arsenical pyrites rich in silver. Much of the gold is very high grade. No mill for reducing the ore has yet been put up. A number of arrastras were working along the creek at the time of my visit, but they save, of course, only the free gold in the decomposed surface ores, the silver being allowed to wash away. The veins in the hard granite are somewhat bunchy, but are numerous and rich. The greatest depth reached, 200 feet, was in the Chicago Mine. The rest of the work done here has been surface work. At the time of my visit there was not enough development to show the character of the deposits.

The road from Igo to Gas Point lies over a smooth gravel ridge, which extends in a southeast direction north of the Cottonwood. South of the Cottonwood the gravel thins out, and has been mined over a large extent of country west of Gas Point. Cretaceous shales outcrop over most of the country between the forks of the Cottonwood. Near Gas Point they are covered by a volcanic ash, which is in turn covered by gravels. The ash is very loose and soft, and in sluicing off the gold-bearing gravels on top, ditches were dug in it. The ash contains fragments of pumice 4 to 5 inches in diameter. The ash has been cut through in places, and between it and the bedrock were found petrified trunks of trees and charred stumps, producing a poor quality of coal. This body of pumice and ash must belong geologically to the great deposit of that character on the west slope of the Sierras, and antedates, of course, the gravel period. A gravel ridge runs east and west for several miles between the North and Middle Forks of the Cottonwood, and it also has been largely mined over. The gravels have been worked to within 2 miles of Anderson. Looking north from this point, the gravel ridge which extends southeast from Igo presents a remarkably even slope, and must have been deposited by Clear Creek, when its volume was much greater than at present.