form to the contact line as it would to a certain degree if deposited on It is worth noticing that the serpentine dikes occur more frequently than anywhere else at the contact of the Cretaceous with the older series, showing a line of weakness at that point. spathic rocks. Farther up the mountain are talcose and argillitic slates. These continue westward along the ridge for several miles without much change, except to become contorted and filled with bunches and veinlets of secondary quartz. These rocks form the summit of the Coast Range, and extend indefinitely westward. The most common strike is north and south. A fine view of the Cretaceous foothills is obtained from the high mountains. The strike of the strata is parallel to the line of upheaval, and owing to the different degrees of hardness there is a succession of valleys and mountains extending in the northwest and southeast direction, with abrupt escarpments to the southwest. A valley has generally been eroded at the western edge of the Cretaceous. On the south bank of Thome's Creek is a sandstone dike similar to those described by J. S. Diller. The Metamorphic Series has here a width of 18 miles east of the divide. The highest points of the divide reach an elevation of 7,000 feet. The serpentine dike narrows before Thome's Creek is reached, and breaks up into smaller ones, with strata of the older series between them. The serpentine is bordered on the east by a large body of fine-grained diorite, which weathers so much more slowly than the shale that its boundary on the east forms the edge of a steep, high ridge for many miles; a very marked feature in the topography of the country. The metamorphic rocks west of the serpentine consist of quartzites, jasper, hornblende schist, and firmly cemented conglomerates. The Cretaceous shales on the east for at least a mile are exceedingly broken, faulted, and folded on each other, producing graceful, wavy lines, both vertically and horizontally. A mile from the edge of the shales there is an outcrop of granular limestone, full of specimens of brachiopods and aucella. The general elevation of the country occupied by the shales about Paskenta is 1,000 feet. A bend in the serpentine at Thome's Creek causes a great curve in the shales, which appear nearly 2 miles farther west on the south side than on the north. The strike of the shales follows the bending appearance appear in the serpentine. in a general way, but it is very broken. At the lower end of the cañon of Thome's Creek a dike of serpentine has been intruded, metamorphosing the shales for nearly 100 feet. They are hardened and impregnated with calcite, having the stratification obliterated for 200 feet. The calcite is, of course, a secondary product, derived from the decomposed serpentine. Evidences of dynamic action are very pronounced in the serpentine. It presents the appearance of a conglomerate, in which nodules of all sizes of fresh serpentine are imbedded in a matrix of crushed serpentine. The edges of the dike are finely laminated and full of slickensides. West of the serpentine are dikes of diorite, dioritic conglomerate, strata of hornblende schist and hornblendic conglomerates, followed by felsite, jasper, and quartzose rocks. Then there is another dike of crushed serpentine, followed by fine diorites, and at some distance up the cañon by massive serpentine. This series of dikes is worthy of far more study than could be given at the time. In the edge of the mountains 1 mile north of Thome's Creek there is an outcrop of gray limestone similar to that farther north. The shales south to Newville and beyond dip very steeply for 2 or 3 miles east of the serpentine, often as high as 75°. Four miles southwest of Newville the serpentine expands again to a width of over 2 miles, forming a long ridge projecting into the valley at a small angle. In it is a deposit of chrome iron in granular form. Bodies of diorite of vary Fine specimens of the fossil aucella occur on Grindstone Creek. A mile south of the creek, and 3 miles west of Stony Creek, the shales rise to a height of 1,400 feet, and are terminated by a dike of serpentine not over 100 feet wide. Pearly talcose schists follow the serpentine for a few hundred feet, when there occurs another dike of serpentine. West of this schists and slates outcrop to the divide. A part of these are green schists, often crumpled and silicified, while the slates are often the jet black variety. So abundant is the quartz that the surface is often covered with the fragments. The strike is very irregular, but averages north 40° to 80° east. The hills are covered with dense brush up to an elevation of 3,000 feet, where the pine timber begins. The black slates are often finely cleavable in pieces of considerable size, and resemble those of the Mother Lode. On Elk Creek, 4 miles west of Stony Creek, the shales come in contact with the black slates and green schists. The shales gradually increase in dip as the contact is approached, finally becoming vertical or reversed. On the Round Valley road the shales extend up the side of the mount-The schists dip east 70° to 80°, strike north 20° to 30°. The change to ain to an elevation of 2,000 feet. Above the shales are dikes of serpen- the vertical green schists is abrupt. Fig. 6 illustrates this contact. tine so badly crushed as to be reduced to powder; alternating with these Toward the crest, 5 miles away, they become more silicified. The clay are hard, fine-grained rocks, jasper, petrosilex, pseudo-diorite, and feld-at the contact has been formed by an upward movement of the meta morphic ridge, a condition noticed at several points farther south, and Along the ridge southeast of Fout's Springs, bunches of the dark aphanitic which to a certain degree obscures the non-conformity. This is undoubt rock, similar to that north of Stony Creek, appear in the slates. The edly the reason for the apparent conformity between aucella-bearing divide at the head of Mill Creek has an elevation of 6,000 feet. This strata and the metamorphics of Mount Diablo, mentioned by Mr. Becke elevation is kept up for 3 or 4 miles to the south, when the ridge turns as a proof of the unity of the two formations. About 100 feet north easterly and sinking below the timber line, becomes covered with heavy the creek a dike of serpentine begins and widens northward. It lie brush. At the head of Mill Creek the rocks strike east and west, and between the schists and the shales. The latter show the usual blacken show a slight amount of silicification. Coarse and fine sandstones abound, ing and hardening near the contact, while in the cañon, where and also actinolite and glaucophane schists. This formation extends serpentine is present, they are simply crushed. The serpentine, where southerly for many miles into Lake County. The topography of Lake not too much decayed, shows the usual foliated pyroxene crystals, and County can be studied to advantage from here. As far as one can see has associated with it fresh hornblendic rocks. to the south and west, the county consists of parallel ridges. No intrusive Serpentine appears again on Griscoe Creek, having a considerable width rocks appear on the ridges at this point. Northward toward Snow It has associated with it dioritic rock and some jasper. West of these Mountain there is much sandstone, and silicification becomes more are the usual dark to pale green schists. prominent. Bunches of serpentine and green diorite occur near Fout's South of Griscoe Creek the metamorphics and serpentine take a more Springs; the former becomes very extensively developed northward along southeasterly course to and past Stony Creek. Between these points the the eastern slope of Mount St. John. On the grade east of the springs shales also change in strike, and are bordered a part of the way by ser there is a good exposure of black slates. These form the country rock pentines, and part by hard, dark, felsitic rocks. Strong salty and sul in the vicinity of the springs. The serpentine is so greatly crushed along phurous springs are common in the shales through this section. A very Stony Creek, north of the springs, as to present soft, greenish clay banks. fine contact between the shales and serpentine is shown on Stony Creek No contact appears, but the serpentine is of course younger than the The shales are much broken for 300 feet, but the stratification is obliter amygdaloidal eruptives forming Mount St. John. ated, and they are distinctly metamorphosed for only 100 feet. They Almost the only rock exposed along the cañon of Stony Creek for a are largely serpentinized and filled with seams of carbonates, so much number of miles is an amygdaloidal eruptive. The amygdules are genso that their original character has entirely disappeared. These second erally small and occur through the rock in bands or layers, undoubtedly ary changes have in part obliterated the effects produced by the molte due to flowage. They consist of chlorite or calcite. Two miles up the dike. Both the altered shale and the serpentine have been rendered cañon, at the very base of Mount St. John, the rock becomes a diorite porfissile by pressure and movement along the walls of the dike. Several phyrite, with pale green feldspar crystals. In places it assumes a granhundred feet from the contact the serpentine becomes massive and show ular structure and appears like a diabase. Orbicular diorite appears in the usual foliated crystals. A quarter of a mile within the serpenting places. For a mile in the cañon the rock is a diorite tuff, whose origin is a body of diorite. The relation of these bodies of diorite to the ser is rather uncertain. The bedding is, as a rule, plainly visible, with a pentine has not yet been investigated. They may be a differentiate slight dip. However, it sometimes becomes compact and massive, and portion of the base magma, or masses of unfused rock caught up in the the pebbles are so nearly blended as to suggest other than a clastic origin. intrusion. Three miles northeast of Stony Ford there is a vein-like This diabase or diorite, as a part of it may be, probably forms the whole deposit of lime in the serpentine, which is being quarried and burned of St. John and the eastern and northern part of Snow Mountain. On The serpentine ridge runs about a mile east of Stony Ford, and the summit and western side of Snow Mountain there is said to be much inclosed in Cretaceous shale. For many miles north of the town red jasper. The two mountains are nearly of equal height, rising about valley has been eroded between the shale and the serpentine. Paralle 7,000 feet. They are the most prominent peaks in this portion of the ranges of hills formed of coarse conglomerates lie farther east. Coast Range. About Stony Ford there is a large area of good land, with plenty of The geology about the head of Stony Creek is quite complex and of water for irrigating. The eastern foothills of Mount St. John are covere very great interest. All the foothill country south of Stony Ford conwith a reddish adobe soil, and underlaid by a dark basic rock, which sists of Cretaceous shale. A large body of serpentine begins in the high seems to be an aphanitic variety of an old and greatly altered eruptive hills southwest of the town and extends in a southeasterly direction This massive rock outcrops along the road to Fout's Springs for a dis between the Cretaceous and the older series. It extends into, and forms tance of 4 miles. It is followed by dull red jasper, and that by serpen the divide west of, Bear Valley. On the head of Little Stony Creek the tine. The latter rock is the southern continuation of a large body of the metamorphics are highly altered, feldspathic and hornblendic schists same composition which has been intruded into the basic rock on th and pseudo-diorites predominating. Bear Valley is one of a series which eastern slope of Mount St. John. The serpentine is followed by pa have been eroded at the contact of the Cretaceous with the serpentine. green quartzose schists, talcose, and black finely cleavable slates, and A line of sandstone and conglomerate hills divide the upper end of Bear sandstone, as far as the summit. In many places through the brush Valley. The pebbles are chiefly jasper, quartz, and petrosilex. The dip hills below the timber line, the slates are only slightly metamorphosed varies from 40° to 70°. Serpentine outcrops at the eastern base of the and might easily be taken for the Cretaceous if it were not for other con divide between Bear Valley and Little Indian Valley. Up the grade it siderations. There is not much silicification nor are the schists great is succeeded by red argillaceous jasper and fresh diorite. Then for a crumpled. The strike is very irregular, east and west to north 60° west mile across the summit only serpentine is seen. A short distance down on the west, shaly slate is encountered. It strikes east and west and obtained in large slabs. Very often the slatiness has been destroyed by less than 100 feet wide. It is followed by serpentine again, and that crushing, and flattened needle-like fragments result. This is particularly soft shales, striking north and south, and a body of sandstone a quartenoticeable where the strike of the slate forms an angle with the line of of a mile across. As a general thing the sandstone is not greatly met upheaval. Of two layers side by side, one is undisturbed, the other morphosed. It is succeeded by more shale and then by serpentine, crushed or twisted out of all semblance, or the undisturbed strata change which are argillitic masses, great and small, together with jaspers an in a few inches in the line of strike into the same condition. Green dikes flinty rocks, quartzites, and dike-like bodies of diorite and feldspath become numerous, and at Allen's Springs a red mineralized stratum, with rocks. Farther still toward the west the serpentine becomes so broke dikes adjoining, seems to show the effect of mineral waters. up by these bunches of rock, which become more metamorphosed, the North of Allen's Springs, the divide between Cache Creek and Bartit assumes the appearance of dikes winding and twisting through th lett's Creek contains dikes of diorite and serpentine. The latter forms a metamorphic rocks. The serpentine is often green, often jet black, wit series of bunchy dikes extending in a northwest direction past Bartlett's a shining metallic luster, caused by the great pressure and movemen Springs. The elevation of the springs is 2,100 feet. The green dikes to which it has been subjected. In many places there is an excellen sometimes assume an amygdaloidal character, showing their intrusive opportunity to study contact phenomena. The sharp line of conta origin. It is often difficult to distinguish these dikes from the green contagorigin. between the serpentine and metamorphics is always to be seen. On the metamorphic schists, when the amygdaloidal character is absent. hillside the serpentine has decayed away, leaving a sharp ridge of har Near Allen's Springs is a stratum of conglomerates interbedded with argillite exposed. In a gulch there rises a vertical cliff of argilliti the slates. The pebbles are chiefly quartz of different kinds; the dip is rock; the serpentine has been eroded, leaving the smooth, hardened, an vertical. Slate forms most of the rock at Bartlett's. Sandstone preblackened surface. The serpentine has often been reduced to a powde dominates in the mountains toward Clear Lake. There are bunches of It is probable that this took place after the serpentinization. The meta diorite and serpentine about Bartlett's which undoubtedly have some morphics have lost their stratification and have been so crushed as connection with the springs. The formation is much the same for many miles northwest of Bart appear but slightly altered. It would be very easy to confuse these slates and sandstones with th lett's, except that in places it is more silicious. There are some glaucoCretaceous in Bear Valley; that is, judging simply from the amount phane schists and small patches of the amygdaloidal green dikes. metamorphism; but I believe they belong to the older series, for no fossil Serpentine also appears in places along the hills south of the North were seen, though carefully looked for, and also because of their position Fork of Cache Creek. On Eel River, 5 miles from Bartlett's, there is a for 2 miles east in the serpentine are jaspers, which are known only large body of red jasper schists filled with secondary quartz veins; also the Pre-Cretaceous rocks. The exceedingly metamorphosed and crystal green chloritic and crumpled schists. This shows that the greatest line bunches in the serpentine probably belong to rocks of that classilicification is not confined to the higher ranges. On the head of the which have been noted so often near the eastern edge of the older series North Fork of Cache Creek a body of soft, black shales is met again. and which were already metamorphosed at the time of the serpentin They are so greatly crushed that the stratification is destroyed, There eruption. These rocks, together with others of the Metamorphic Serie is no question but that these as well as other occurrences are an integral were broken in fragments by the intrusive magma, and enveloped by part of the older series, but the crushing they have undergone has given The small metamorphosing power of this basic magma is also to them the appearance of less metamorphism. In fact, it seems that with noticed. I know of no more interesting spot in the whole Coast Range almost any degree of metamorphism, slates maintain much the same for the study of serpentine and its relation to the older series. Thappearance, and thus in the orographic movements the argillaceous rocks theory of the metamorphic origin of serpentine itself receives no suppon The serpentine on the head of Eel River is crushed to a green clay, or are far more apt to be crushed than the more quartzose ones. A little east of Stanton's, in Little Indian Valley, a body of the gree the bed of the creek, with argillaceous shale on both sides. The springs shining black shales. At Crabtree Springs the serpentine is exposed in quartzose schists appears in the serpentine. This is the rock traced con come up at the contact as well as in the serpentine. There is an immense tinuously south from Bully Choop. The surface near this outcrop amount of carbonic acid gas bubbling up through the water of the creek covered with quartz from the small veins with which the schist is filled and that which flows out of the hillside. The noise of the escaping gas The serpentine outcrops along the road nearly to Cache Creek, and seem from the phenomena. to form the greater portion of the hills east of the creek, and south on coming down to the creek to drink. Iron, soda, and sulphur springs Little Indian Valley. The serpentine narrows to the north, and the divide 3 or 4 miles from Stanton's is formed of the metamorphic rocks. Pebbles of the gree wavy schists filled with quartz veins are numerous in the creek, whic rises north of Little Indian Valley. Sandstone is the first rock foun outcropping on Cache Creek; strike north 30° west, dip vertical. In are dikes of a green eruptive. For several miles up to the mouth Bartlett's Creek the rocks are chiefly slates and sandstones, striking nor 40° to 60° west. The slates are usually finely cleavable, and can can be heard some distance. Birds and small animals are often killed It appears that all the springs of this section are situated nearly in ance is, however, no criterion, as the rocks are softened to a considerable line extending northwest from Hough's Springs, and near or on the lin depth. Fresh pieces are quite hard and compact. Many amygdaloidal of the serpentine intrusives. intrusives, somewhat similar to those about Bartlett's, are scattered Sandstone is the prevailing rock exposed along the north side of th through the hills about Scott Valley. Some are porphyritic with feldmountain between Bartlett's Springs and Upper Lake. The strike an spar, and others contain large or very minute amygdules. dip are seldom noticeable, but the rocks are cut up by jointing plane Between Upper Lake and Lakeport there is a large body of serpentine. More slates appear on the south side of the range, and down to the To Slates, with the usual strike and vertical dip, were also seen. Between House form the larger part of the rock; they generally dip at a hig Upper Lake and Morrison's the rocks are exposed in places nearly to the angle to the north, strike with the mountain range, northwest and south water's edge. They seem to be chiefly sandstones, with jasper higher on east. The height of the range is 4,000 feet. A mile and a half abo the ridge. A mile east of Upper Lake there is a cropping of coarse diorite, the Toll House the black slates are crushed to a mass, into which the containing hornblende crystals a half inch in diameter. This extends broken sandstone strata have been squeezed, so that fragments lie wholl east for some distance, but is generally fine grained and might easily be inclosed in the black clayey mass. The shales also contain small bodi taken for a metamorphic sandstone. As a matter of fact, the sandstone of metamorphic limestone. No intrusive rock, except a small area shows no tendency to become crystalline. The valley of Clear Lake has serpentine near the summit, and a body of green dioritic character of been eroded in the sandstone and shale of the older series where they the southern slope, was seen. Actinolite in finely crystallized masse were least metamorphosed, and consequently more easily washed away. occurs on the summit. The ridge south of Clover Creek, extending A careful search was made for fossils, a mile and a half east of Mortoward Upper Lake, is formed largely of jasper. Several bodies of ser rison's, where W. A. Goodyear had mentioned seeing some, but nothing pentine occur in it a mile east of Upper Lake. A ridge of soft sandston was found, save some small impressions of plant stems, one eighth of an begins a mile northwest of Upper Lake, and extends northwesterly fo inch in diameter, straight and jointed. The sandstone and shale do not about 10 miles between Middle Creek and Bachelor Valley. It rises dip at a high angle, in places being nearly level, and to all appearances perhaps 1,000 feet above Clear Lake. The strata are thick bedded an are but slightly metamorphosed. almost level, and are underlaid by the argillites of the older serie which replace the sandstone on the northwest. It contains no fossil but from its resemblance to the fossiliferous Chico-Tejon sandstones ne Lower Lake, it is judged to be of that period. Banded jaspers a abundant along the north side of Middle Creek. They are often way and filled with secondary seams of quartz. An artesian belt extends north and south through Upper Lake. Quicksilver has been found on the lake shore near Morrison's, and two tunnels run. The deposit seems to have no relation to intrusive rocks, unless one near the entrance to the tunnel be a greatly decomposed diorite. It is filled with calcite seams. From this point the new toll road was followed to the summit, and from there a road leads to High Valley. The eastern end of the valley is covered with basalt, which ́extends east to the North Fork of Cache Creek. Basalt occurs northeast is about 5 miles long and three fourths of a mile wide. Water Water of the Sulphur Bank, and also at the mines. Here it has been decomobtained at a depth of 60 to 70 feet, and will rise 20 feet above the posed over a large area near the water's edge by solfataric action. In surface. It is found under a bed of clay, or in some cases cemente places the decomposition is complete; in others it has operated only gravel. The water-bearing strata extend up Middle Creek, the gradua along cracks or seams in the basalt, leaving large rounded bowlders of rise giving the pressure. No surface water flows in this or Clove the fresh rock with concentric shells formed of the whitish secondary Creek. The basin is quite limited, for when new wells are put down the product. Sulphur and cinnabar have been deposited in the decomposed others are weakened. portions. Where decomposition has been complete amorphous silica is The rocks along the northern side of Bachelor Valley are slates, whid the most important residuary product. The cavities of the basalt, where have been much crushed. Toward the Blue Lakes sandstone prunaltered, contain more or less of opaline quartz, and bunches of acicular dominates. crystals of aragonite. The work here now is confined exclusively to the The Blue Lakes are in a deep, narrow cañon, and almost on a lev surface. Great pits and trenches have been dug as the quicksilver has with Clear Lake, with which they must have been once connected, eithe been traced from point to point in the decomposed portions of the basalt. by Tule Lake or Scott Valley. The latter runs northwest from a poi It is supposed that the deposit of quicksilver is still going on, and, on 2 miles west of Lakeport, and is separated from the lake by low cla many accounts, it is a very interesting place for the mineralogist. and gravel hills. The lakes are located in what once must have bee Big Valley is formed by Quaternary deposits, formerly the bed of the outlet of Clear Lake when it emptied toward the west. The lake Clear Lake. It covers the region about the lake between Kelsey and have been formed by the filling up of this old cañon from side gulche Adobe Creeks. At Kelseyville is a little knoll several hundred feet across, This fact is finely illustrated at the Blue Lakes Hotel, where the tw out of which illuminating gas has seeped. A well was bored here to a main lakes are separated by a body of detritus from cañons on opposit depth of 160 feet, passing through blue clay and some gravel. On striksides. The lakes are said to be over 200 feet deep. A slight elevatio ing sandstone an abundant flow of gas and mineral water was met. of the mountains on the west must have been sufficient to turn the lak first the force was so great that the water rose 15 feet above the top of a eastward into Cache Creek. 20-foot pipe. The water is evidently brought up by the gas. Wells have been bored to a depth of 400 feet at a distance of a mile north and west, but nothing of this kind was found. Nearly all the rocks exposed through Scott Valley are sandstone often shaly and soft, with no distinct stratification. The surface appea At GEOLOGY OF TEHAMA, COLUSA, LAKE, AND NAPA COUNTIES. 65 The Quaternary clays, hardened almost to a shale, outcrop in the hill minerals, and seems to have been the last substance deposited in any between Kelsey and Adobe Creeks. They reach an elevation of 500 fee quantity. above the lake, and apparently overlie the obsidian tufas. The Meta An old mine across the creek from the Bradford is located in sandstone, morphic Series outcrops about a mile east of Highland Springs. It con which is to be seen on the dump. Dr. Becker speaks of it as unmetamorsists of massive sandstone, banded quartzite, and jasper. Farther south phosed and representative of the Cretaceous, but it has undoubtedly serpentine outcrops between Kelsey and Adobe Creeks. Beautifully become soft through decay and belongs to the older series. banded obsidian outcrops along the road to Cobb Valley for a distance Serpentine is the chief rock exposed along the road for 2 miles above of 4 miles, reaching nearly to the summit. White ash is often inter the Bradford Mine. The hills on the east are formed of the same rock stratified with it. Slaty lavas form the top of the mountain, which has until the volcanic deposits hide it from observation. The serpentine by an elevation of 3,000 feet. Serpentine is met on the southern slope of the the road incloses bunches and dike-like masses of diorite of varying mountain. This rock outcrops for many miles through the hills east of degrees of crystallization, and also seems of a dark aphanitic material, Cobb Valley, reaching in its southern extension nearly to Middletown. A which may simply be finer portions of the serpentine. The serpentine large part of it has been reduced to a clayey powder, in which rest nod is very much decayed, but instead of being crushed to a clay, it shows a ules of the massive rock. Volcanic rocks cover Mount Cobb and extend jointed structure, breaking up into small angular fragments. It decays down to the road on the divide northwest of Middletown. Metamor on the surface to a yellowish mass, very strongly resembling a soft sandphic sandstones, greatly crushed, outcrop along the road to Middletown stone. This of course is a resemblance merely, which has deceived many They are jointed and crushed. There is a large extent of serpentine with regard to the origin of serpentine. The diorite does not seem to be south of the town in the vicinity of the quicksilver mines. The altered sandstone, for no transition has been observed. It belongs either rocks exposed along the road which leads up to the Great Western Mine to dikes intruded into the serpentine, or to deep-seated crystalline rocks belong to the older series, and are considerably metamorphosed. Glau brought to the surface with the melted magma. The serpentine has cophane schists, banded quartzose rocks, and green schists predominate never been noticed to have any great metamorphosing power. The stratification is generally destroyed, but when present it is quite flat Thick deposits of white volcanic ash cover the ridge toward the Oat dip varies from northwest to southwest. The mine is located on the con Hill Mines. Two miles west of the mines it is replaced by andesite and tact of greenish quartzose schists with silicified serpentine. The or basalt. The bedrock, wherever exposed, is a soft, light-colored sandoccurs on flinty opaline strata, which probably belong to the Metamorphic stone, and shale. Where it is not capped by lava it shows a dip of 30° Series, and also in seams in the silicified serpentine. The serpentine is to 40° north, strike east and west. The strata silicified to quite a distance, and veins of opaline matter run through it The Oat Hill Mines are located in a body of soft sandstone, which beyond where it is completely altered. The mountain range forming the was first noticed 2 miles to the west. It extends nearly to Pope Valley western boundary of the county consists of the usual jasper and sand and has a width of about a mile. On the east it blends gradually into stone, with some hornblende schist. metamorphic sandstone. The Bradford Mine is located on a deposit which occurs chiefly at the the hill lying east of the works. North of the lava-capped ridge are hard This is clearly shown on the western slope of contact of silicified shale and serpentine. The ore occurs in parargillites, turning to green and red jasper, filled with minute veinlets of impregnating a black to light-colored opaline sinter, which seems to quartz. The black argillites are also somewhat silicified. represent the total replacement of the serpentine; and in part the dip at a high angle to the north, and a mile away to the northeast they impregnation of the silicified foot wall, which was originally an argillite are followed by granular serpentine. In places the serpentine has A wedge-shaped dike of serpentine lies at the northern end of the work undergone such pressure, accompanied by movement, that it has become ings and divides the ore deposit. Serpentine is met also at the southern a mass of tough, welded fibers. Coarse hornblendic rocks are associated Between these points the ore occurs in silicified metamorphi with the serpentine. All the observations made about the Oat Hill rocks. The ore body pitches to the southeast, the mineralized stratum Mines show conclusively that these soft sandstones belong to the older to the east. The body of ore worked has a thickness of 50 feet at the series. widest part, and a length of 300 feet. The main deposit lies on the foot For some unknown reason this strip of country, of which the Oat Hill wall or in the form of veins running down vertically or dipping toward Mines are about the center, has escaped the prevailing metamorphism. it. The ore occurs, as in other mines, in seams in the crushed gangue No signs of any intrusive rock are to be found in any of the workings of though it is sometimes scattered through the hard, massive portions the mines, and the occurrence of extensive cinnabar deposits wholly in and then must have been deposited at the same time as the silica in sandstone and shale is an anomaly. The veins run generally about which it is inclosed. Two periods of deposition are thus represented north 22° west, dip to the northeast. Three veins are worked in the They are separated by a time of movement and crushing in the vein Eureka Mine, one of which runs southwest. The ore occurs as veins In places there is found a considerable amount of native mercury and and impregnations in the sandstones. Wherever the ore occurs in the some sulphur. North of the workings is another ore body, 90 fee form of defined veins, it is usually associated with or has a gangue of long and 20 feet thick. Calcite and quartz seams run through the rock hard flinty rock, not opaline, as is usually the case. and into the foot wall. Much iron pyrite is present in the mine, and lies on the foot wall, but separated from it at times by a heavy layer of in the vicinity of the larger masses the workings are much warmer clay. However, this tough layer of clay is more often found on the owing to the oxidation. The pyrite coats the deposits of the other hanging wall. Owing to this clay on the hanging wall, the large veins This hard stratum |