The Quaternary clays, hardened almost to a shale, outcrop in the hills between Kelsey and Adobe Creeks. They reach an elevation of 500 feet above the lake, and apparently overlie the obsidian tufas. The Metamorphic Series outcrops about a mile east of Highland Springs. It consists of massive sandstone, banded quartzite, and jasper. Farther south serpentine outcrops between Kelsey and Adobe Creeks. Beautifully banded obsidian outcrops along the road to Cobb Valley for a distance of 4 miles, reaching nearly to the summit. White ash is often interstratified with it. Slaty lavas form the top of the mountain, which has an elevation of 3,000 feet. Serpentine is met on the southern slope of the mountain. This rock outcrops for many miles through the hills east of Cobb Valley, reaching in its southern extension nearly to Middletown. A large part of it has been reduced to a clayey powder, in which rest nodules of the massive rock. Volcanic rocks cover Mount Cobb and extend down to the road on the divide northwest of Middletown. Metamorphic sandstones, greatly crushed, outcrop along the road to Middletown. They are jointed and crushed. There is a large extent of serpentine south of the town in the vicinity of the quicksilver mines. The rocks exposed along the road which leads up to the Great Western Mine belong to the older series, and are considerably metamorphosed. Glaucophane schists, banded quartzose rocks, and green schists predominate. The stratification is generally destroyed, but when present it is quite flat; dip varies from northwest to southwest. The mine is located on the contact of greenish quartzose schists with silicified serpentine. The ore occurs on flinty opaline strata, which probably belong to the Metamorphic Series, and also in seams in the silicified serpentine. The serpentine is silicified to quite a distance, and veins of opaline matter run through it beyond where it is completely altered. The mountain range forming the western boundary of the county consists of the usual jasper and sandstone, with some hornblende schist.

The Bradford Mine is located on a deposit which occurs chiefly at the contact of silicified shale and serpentine. The ore occurs in part impregnating a black to light-colored opaline sinter, which seems to represent the total replacement of the serpentine; and in part the impregnation of the silicified foot wall, which was originally an argillite. A wedge-shaped dike of serpentine lies at the northern end of the workings and divides the ore deposit. Serpentine is met also at the southern end. Between these points the ore occurs in silicified metamorphic rocks. The ore body pitches to the southeast, the mineralized stratum to the east. The body of ore worked has a thickness of 50 feet at the widest part, and a length of 300 feet. The main deposit lies on the foot wall or in the form of veins running down vertically or dipping toward it. The ore occurs, as in other mines, in seams in the crushed gangue, though it is sometimes scattered through the hard, massive portions, and then must have been deposited at the same time as the silica in which it is inclosed. Two periods of deposition are thus represented. They are separated by a time of movement and crushing in the vein. In places there is found a considerable amount of native mercury and some sulphur. North of the workings is another ore body, 90 feet long and 20 feet thick. Calcite and quartz seams run through the rock and into the foot wall. Much iron pyrite is present in the mine, and in the vicinity of the larger masses the workings are much warmer, owing to the oxidation. The pyrite coats the deposits of the other

minerals, and seems to have been the last substance deposited in any quantity.

An old mine across the creek from the Bradford is located in sandstone, which is to be seen on the dump. Dr. Becker speaks of it as unmetamorphosed and representative of the Cretaceous, but it has undoubtedly become soft through decay and belongs to the older series.

Serpentine is the chief rock exposed along the road for 2 miles above. the Bradford Mine. The hills on the east are formed of the same rock until the volcanic deposits hide it from observation. The serpentine by the road incloses bunches and dike-like masses of diorite of varying degrees of crystallization, and also seems of a dark aphanitic material, which may simply be finer portions of the serpentine. The serpentine is very much decayed, but instead of being crushed to a clay, it shows a jointed structure, breaking up into small angular fragments. It decays on the surface to a yellowish mass, very strongly resembling a soft sandstone. This of course is a resemblance merely, which has deceived many with regard to the origin of serpentine. The diorite does not seem to be altered sandstone, for no transition has been observed. It belongs either to dikes intruded into the serpentine, or to deep-seated crystalline rocks brought to the surface with the melted magma. The serpentine has never been noticed to have any great metamorphosing power.

Thick deposits of white volcanic ash cover the ridge toward the Oat Hill Mines. Two miles west of the mines it is replaced by andesite and basalt. The bedrock, wherever exposed, is a soft, light-colored sandstone, and shale. Where it is not capped by lava it shows a dip of 30° to 40° north, strike east and west.

The Oat Hill Mines are located in a body of soft sandstone, which was first noticed 2 miles to the west. It extends nearly to Pope Valley and has a width of about a mile. On the east it blends gradually into metamorphic sandstone. This is clearly shown on the western slope of the hill lying east of the works. North of the lava-capped ridge are hard argillites, turning to green and red jasper, filled with minute veinlets of quartz. The black argillites are also somewhat silicified. The strata. dip at a high angle to the north, and a mile away to the northeast they are followed by granular serpentine. In places the serpentine has undergone such pressure, accompanied by movement, that it has become a mass of tough, welded fibers. Coarse hornblendic rocks are associated with the serpentine. All the observations made about the Oat Hill Mines show conclusively that these soft sandstones belong to the older series.

For some unknown reason this strip of country, of which the Oat Hill Mines are about the center, has escaped the prevailing metamorphism. No signs of any intrusive rock are to be found in any of the workings of the mines, and the occurrence of extensive cinnabar deposits wholly in sandstone and shale is an anomaly. The veins run generally about north 22° west, dip to the northeast. Three veins are worked in the Eureka Mine, one of which runs southwest. The ore occurs as veins and impregnations in the sandstones. Wherever the ore occurs in the form of defined veins, it is usually associated with or has a gangue of hard flinty rock, not opaline, as is usually the case. This hard stratum lies on the foot wall, but separated from it at times by a heavy layer of clay. However, this tough layer of clay is more often found on the hanging wall. Owing to this clay on the hanging wall, the large veins

and chief impregnations often extend out into the foot wall. Outside of the clay on the hanging wall, no mineralization has taken place. In places the main vein reaches a width of 80 feet. It consists of the impregnation of the soft sandstone. Often the ore is visible only when the rock is scraped, thus crushing the crystals of cinnabar and producing a red streak. This is the test employed in the mine to determine whether the ore is present or not. There are also seams of granular sand, richly impregnated with cinnabar. It is probable that the water which once circulated through the seams abstracted the clay, leaving the clean sand, for it has been noticed that in many places on the hillside, wherever there are signs of solfataric action, just below are deposits of fine clay. One ore shoot has been found to be 500 feet long; the ore running southwest over 300 feet, and very regular. Wherever the sandstone is very hard, the ore is found in the comparatively narrow seams. When there is not much clayey matter, and the sandstones are soft, they are impregnated for a great width. No native sulphur is found here. In the tunnels not worked for several years there forms a heavy deposit of epsomite in fibrous aggregates. It is 4 inches deep in places on the bottom of the tunnel. The north ends of the veins in the Eureka claim show a tendency to swing toward the west and southwest. A breccia of sandstone fragments, mixed with clay, is often found. The strata are very finely banded and somewhat silicified in places. Small quartz seams appear at times, but show no relation to the ore deposits. Shaly sandstones appear near the northern base of the mountain. They are but slightly altered and dip in various directions.

Near the eastern end of the Calloyami ranch appears tawny, heavybedded sandstone. It undoubtedly belongs to the Chico-Tejon series. Northward, along the road to Guenoc, this sandstone appears in mass resting on the serpentine, which forms a line of hills between the Guenoc and Calloyami ranches. It is also extensively developed along Seigler Creek. They are so thick bedded that the dip is quite indistinct, but it is probably southwest at a small angle. The sandstone forms a line of hills north of Harbin Springs. A little farther toward Guenoc, but not directly in contact with the Chico, are shales and hard feldspathic sandstones belonging to the older series; dip east 15° to 20°. These are followed by serpentine. Putah Creek flows out of the valley through a deep cañon formed of stratified basalt cliffs. These extend nearly to the mouth of Soda Creek, so that no contact between the Cretaceous and the older rocks could be found. Some float gold is found in the hills southeast of Guenoc, but its source has not been found. Chico sandstone underlies much of the volcanic country between Seigler Creek and Lower Lake.

The valley of Soda Creek is bounded on the west by an abrupt tableland of basalt. Three miles from Lower Lake soft sandstones appear and cover the country to the town, except a small outcrop of the metamorphics 2 miles southeast. The latter rocks consist of hard green schists. Though no actual contact was observed, on account of the great amount of soil, yet there is not the slightest doubt of an unconformability. About the head of Soda Creek these Chico-Tejon sandstones overlie the Knoxville shales, but whether conformably or not is uncertain. The sandstone extends 4 miles north of Cache Creek. Two miles below Lower Lake the creek has cut a narrow cañon through this formation. The strike is north 10° west, dip 70° east. This high degree of

dip makes it more than ever uncertain what its relation is to the Knoxville series. If it is unconformable with the Knoxville there has been a very great upheaval since the Cretaceous. Although there has not yet been found positively an unconformity between the Chico and the Knoxville, yet from the very fact that the serpentine has been intruded through the Knoxville, but not through the Chico, shows that there must be one. From the relative amount of disturbance exhibited by the Chico and Knoxville beds, it is probable that the latter was intruded and somewhat tilted before the deposition of the Chico. Although these formations are apparently conformable in Tehama County, and have been stated to be so by J. S. Diller, yet the Chico lies on the eastern edge of the great Cretaceous deposits, which are fully 5 miles thick, and being so far from the mountains where the elevation and extrusion of the serpentine took place, the Horsetown shales on which they were afterward deposited did not experience the tilting of the Knoxville beds, which lay against the flanks of the mountains. Hence, they were deposited apparently conformable, though a hiatus really exists. The Chico sandstone appears along the road to Seigler Springs. It is often tilted at a high angle, at times vertical, with varying strike. Between this and the basalt forming the higher hills is a small outcrop of jasper and hard chloritic and argillaceous schists. The rocks are jointed and contain vein-like quartz deposits.

A large number of fossils are found in the Chico sandstones about Lower Lake. The sandstones outcrop along the road to Knoxville for many miles, particularly prominent in the ridges between the road and Cache Creek. Three miles east of Lower Lake small patches of a green metamorphic rock project through the Cretaceous. Five miles east a silicified dike of serpentine appears on the hills on the north, and extends southeast past the Baker Mine. It has been altered to a black shining glass, containing green patches of the original rock. The Baker Mine is located on this dike. The cinnabar is found as an impregnation in a crushed zone running north 10° west, and having a width of 8 to 20 feet. It is found over a length of 3,000 feet. The ore deposit is almost wholly an impregnation. From the main body little seams of the ore extend out through lines of fracture in the serpentine. The dike is inclosed in clay derived from the crushing of the Cretaceous shales. The ore deposit pitches northeast 30°. In many places the cinnabar is intimately mixed with iron pyrites, or coat seams of the same mineral.

One mile down the road, on the head of Soda Creek, is a very interesting exposure. The metamorphic rocks, consisting of hard, massive, but jointed sandstone, outcrop in a high bluff south of the creek. It breaks in small angular fragments and is seamed with quartz. A dike of aphanitic diorite has been intruded into the sandstone. Forming the north side of the creek, but hidden in the bottom by a slide of Chico sandstone bowlders from above, is a cropping of the Knoxville shales and fine sandstone. They strike parallel to the junction, a little west of north, and dip to the east at an angle of 30°. They are wholly unaltered, and carry well-preserved specimens of aucella (Fig. 7). Other specimens of aucella were found along the road a short distance east. This outcrop of the Metamorphic Series extends toward the southeast; how far, is not known.

The sandstones on the top of the hill a quarter of a mile north dip and strike about the same as the Knoxville, and half a mile east along

the road they replace the Knoxville shales. The change is indicated by the color of the soil, for the outcrops are not good. It is not certain what the relation of the two formations here is, but they are thought to be unconformable. Chico sandstone outcrops along the ridge between Morgan Valley and the head of Soda Creek, dipping 10° to 30° northeast. With the sandstones are some shales and concretions. South of Morgan Valley are large, flat hills, capped with stratified basalt. It is very fine grained, jet black, and gives a ringing sound when struck. Three miles east of Morgan Valley is an impure limestone, containing fossils, probably Chico. Between this point and Knoxville is a series of little valleys, with a high serpentine ridge on the north between them and Cache Creek. Serpentine also appears in the hills south, extending in a southeast direction. Associated with it are some bodies of metamorphic rocks, jasper, and other characteristic schists. The Chico beds extend from Morgan Valley about 4 miles southeast between these ridges. About 4 miles northwest of Knoxville there is a very puzzling mixture of serpentine, metamorphic rocks, and Cretaceous shale. The road passes in a southeasterly direction for a mile through some small valleys eroded in a narrow stratum of shale, dipping northeast, which evidently belongs to the Knoxville beds. South of the road is a long, narrow strip of massive metamorphic rocks and schists; while on the north is serpentine, containing numerous bunches of massive schistose, semi-crystalline rocks.

From Knoxville north to the Reed Mine and beyond the valleys have been eroded at the contact of the serpentine with the Cretaceous shale. East of the Reed Mine is one small area of serpentine, but the high parallel ridges between this point and Capay Valley are formed wholly of Cretaceous sandstone and shale, dipping to the northeast at a high angle. The Cretaceous shales stand vertical in the bed of North Fork of Davis Creek. The ore of the Reed Mine lies in a zone of crushed and silicified serpentine. The ore occurs in vein form, and in bunches and impregnations, very similar to the deposits of the other mines with similar walls. At the open cut above the old works a body of fine ground diorite rises in a high-pointed peak on the west side of the vein. It extends northward in dike form, appearing on the northeast or hanging wall side in several detached outcrops. The hanging wall in places is a dark, jaspery rock. A short distance east is a stratum of conglomerate, interbedded with the shale. The pebbles are quartzose, and are filled with minute quartz veinlets. This is another indication that