USA > California > Amador County > History of Amador County, California, with illustrations and biographical sketches of its prominent men and pioneers > Part 31
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Metamorphic Slates.
(1)
Metamorphic Slates
The Great Mother Lode of California.
Serpentine Range.
HISTORY OF AMADOR COUNTY, CALIFORNIA.
135
GEOLOGY OF AMADOR COUNTY.
It must not be supposed that any stratum pre- serves a uniform character for any distance. Only a few of the great veins or ranges like the serpentine and the other metamorphie can be traeed in this way. Whether from currents in the ocean deposit- ing different materials previous to the upturning of the slates, or from subsequent ehange by translation of minerals, or both, the slates change in character every mile or two. The black slate will change to gray, then to quartzose, or perhaps to syenite. The metamorphic is often thinned out by other rocks. In some place the serpentine is two miles wide, in others nearly wanting, so that a description of rocks at lone might not fully apply to the rocks four or five miles further north.
The metamorphic rocks near Ione, Lancha Plana and Buena Vista, which have been referred to before, may be taken as a starting-point. These do not form a continuous reef, but here stand as detached masses probably eroded as before mentioned by the waves of the sea. Along the junction of this with the black slate are some of the largest quartz veins in the county. One of them may be seen near Randal's ranch near Ione, one at Mrs. Nichol's place near Buena Vista, and at several other places. That one on Randal's ranch has been sunk on some eighty feet or more without finding anything of value. Where these veins have been subjected to sea wash, as at Mulctown, and, perhaps, the Arkansas diggings, they have made good placer mining. Irish Hill was enriehed by a mountain stream, as the gravel is com- posed of entirely different rocks from that of Mule- town. The hill east of lone is probably sea wash, of the same age as the Muletown deposit. The sea- shore line may be easily traced by the bench-like erosions.
Near the foot-wall of this belt are the Cosumnes, the Arroyo Seco, Lancha Plana, and other copper mines. On the opposite side of this belt is the New- ton copper mine, as well as several others of promise. The reader is requested to note the fact of paying mines being found in the vicinity of these hard slates, though these slates themselves scarcely ever contain any mineral of value. In the intermediate space are many veins containing copper and other minerals in small quantities. Near the Boston ranch some small veins of quartz are estimated to have five dollars to the ton, but they seem to thin out and ramify through the ground so as to be unprofitable to work, though many ravines have been enriched by them. Some veins of steatite (soap-stone) have eon- siderable gold in them visible to the eye, but no one, as yet, has been able to separate it. The gulches running from this range have been rich. Near Irish Hill is the Kirkendall district which was thought to be rich in quartz veins, but the expectations have not been realized.
SERPENTINE RANGE.
This is a striking formation of metamorphic rock, so twisted, contorted and scraggy, that it has been
considered by many as of volcanic origin. The point between Jackson and Stony Creek was thought to be an old crater. A close investigation shows it to be slate, and the ragged, contorted appearance to be the result of the substitution of magnesia for potash in the com- position of the rock. Chromate of iron abounds in it, a vein of it near the Westfalls' ranch being nearly three feet thick. Hundreds of small quartz veins, as well as other ore chimneys, may be seen within a mile or two while walking along this range. Vogan has used many of these veins for road material. When sunk on they often turn to clay, and many of them arc known by being sinks in the ground, or sometimes pot-holes of clay. Silver, gold, and copper are all found in these chimneys in small quan- titics. They were formerly explored for copper. These ore deposits may be a continuation of those found on the west side of the lower metaliferous range. Farther east arc many small quartz veins with considerable gold, though the veins are too nar- row to be worked with profit. Limestone is found in. many places on this range. Not far from the Filmer ranch is a large deposit which burns into good lime; though many of the deposits contain too much silica or magnesia for that purpose, being perhaps a kind of dolomite. It is too dark colored and too hard for ornamental purposes. On the Mokelumne river, near the head of the Laneha Plana ditch, is a curious formation of lime, resembling a frozen waterfall. It is somewhat obscured by the dirt which has fallen over it, but is well worth an examination.
A short distance below is an iron spring, a good il- lustration of an active ore deposit, a formation of iron ore constantly going on, which is every year carried away by the high waters of the river. The ore is probably the result of the percolation of water through decomposing sulphurets not far away. Passing east we strike another belt of metamorphic slates in places two miles in width. This may be considered the great foot-wall of the Mother Lode, also the most prominent indication of the largest valley, following the ranges of mountains, that existed in this county. As the Mother Lode has been, and is now, perhaps, the source of more gold than any space of the same width and length in the world, and, from its having been worked deeper and better than any other place, furnishes more material for a scientific account of the formation of quartz veins, the eonsideration of it will be deferred to another chapter. It may be said of it that it probably fur- nished the gold with which the streams once running parallel to it were enriched, as well as the streams which now cross it, also the larger part of the gold that enriched the gravel diggings at the foot- hills. It is probable that the stream debouched into the Mokclumne or through that depression for a long time before the volcanic era, as there are no large deposits of gravel along the foot-hills near the outlet of the present streams that are of sufficient amount to have been produced by its wash.
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HISTORY OF AMADOR COUNTY, CALIFORNIA.
East of the Mother Lode, which must be consid- ered never less than two hundred. and sometimes two thousand, feet wide, there is little quartz that has any valne. We find veins of slate and syenite alternating with each other. Some of the gulches are enriched by the wash of the great streams of gravel that resulted in the breaking up of the first system of rivers. Nearly half of the ground around Pine Grove seems to be a relic of this wash; streams of gravel, some rich and some nearly barren, traversing the hills in all possible directions. The quartz veins near the last metamorphic range spoken of are prob- ably connected by a sort of geological, umbilical cord with the Mother Lode, though vastly inferior to it in wealth. The veins have not regularity of pitch or strike, sometimes breaking through the slate across the rift and frequently losing themselves in extensive ramifications. In places they are very rich, thirty or forty dollars per ton not being uncommon.
CHAPTER XXVI. GEOLOGY OF AMADOR COUNTY. BY GEORGE MADEIRA.
Extensive Character of the Subject-Mother Lode-Methods of Vein Deposits-Character of the Veins East of the Mother Lode-Minerals in the Tertiary Rocks-Nature of the Limestones-Gravel Deposits-Nature of the Supposed Photographic Rock-Evidences of Glaciers- Moving Large Rocks-Volcanoes-Origin of the Trap Rock-Origin of the Smaller Quartz Veins -- Butte Mountain -Copper-Iron -Gypsum-Asbestos-Marble-Kaolin-Manganese -- Agate -Chalcedony-Skeletons of the Megatherium-Other Fos- sils-Rhinoceros-Hippopotamus-Horse Destruction of the Arcadian Land -- Botany.
[THE following chapter on technieal geology, by a professional mining expert, will please the more scientific of the readers of this work. The writer is amply competent to write an extended and exhaustive treatise on the subject of geology or practical mining .- EDITOR.]
To the geologist and mining explorer, Amador county offers the most interesting field of research to be found in the State, containing, as it does within its limits, the most extensive quartz deposits to be found on the western slope of the Sierras. The great Mother Lode passes entirely across the county in a northerly and southerly direction. At the Keystone mine (Amador) the course of the vein is: south forty-two degrees, twenty-six minutes east; north forty-two degrees, twenty-six minutes west. Inclination of east wall of fissure, fifty degrees; the east hanging wall is a metamorphic silicious slate; and what is known, along the lode, as the west wall rock, or foot-wall, is a blue-black, laminated slate. These laminated slates on the west may not be the true foot-wall, as we find, one- fourth of a mile to the west, a simalar parellel wall of metamorphic slate, although it does not contain the silica found in the east wall rock.
Between these widely divided parallel walls of metamorphic slates, we find numerous stringers of
quartz, from the width of a knife-blade to many feet. The main Mother Lode, however, is found run- ning along the east hanging-wall rock, but in some instances it leaves the same and varies to the west. In the Keystone, at Amador, the vein leaves the cast wall, and, for a space of four hundred feet, does not return to it. In the same mine we find the entire width of the quartz deposit, as far as penetrated to the west, nearly one hundred and fifty feet. At the Empire mine, Plymouth, the vein is seventy-five feet in width. At the Zeile mine, one-half mile south of Jackson, the vein is thirty to forty feet at its greatest width.
Stringers and fceders, from the country rock in geological times, earried the silicious waters to the main fissure, where it deposited its lode of silica that went to form the vein. This lode gives indubit- able evidence of the manner in which it was formed, to wit: by infiltration from the country rock, mostly from the east. The east hanging-wall, in many places along the line of the fissure, is a crystalline, metamorphic slate, which has been changed by heat and pressure into a near approach to diorite. These slates are silicious rather than talcose, and frequently pass into rock closely resembling diorite or trap, and are difficult to distinguish from the intrusive or eruptive rocks. They, at times, assume a porphyritic structure, and may be taken for eruptive rocks.
As we pass to the west, we find the slates grad- ully change from metamorphic, to laminated, then to conglomerate slate,* a series of fragmental rocks. These conglomerate slates have caused much com- ment among explorers, other than geologists, as to their origin, and as they are abundant to the west of the great Mother Lode, but are not found to the east of it, we will give their origin.
These slates are made up of quartz pebbles, fragments of slate, mica, and feldspar. They appear as stratified gravel deposits, and gold has been found in them. These strata were formed on the bottom of a jurassie sea, and are the cemented fragments torn from older rocks. In the upheaval of the Sierras, these slates escaped the pressure that was brought to bear on those further to the east, and hence we find them to-day a series of conglomerate slate and sandstone. It is interesting to pass over these slates, eastward, and see them pass gradu- ally into the metamorphic slates, and trace the out- lines of the quartz pebble in the firm silicious slate along the great fissure that contains the Mother Lode.
At some period, after the jurassic era, the upheaval of the Sierra fissured the western slope, as it is known to have fissured the eastern, with numerous large and small openings. Along the line of the then base of the Sierras, volumes of steam and streams of silicious waters poured from the great fissure, which now contains the Mother Lode. The
*May be seen in quantity near Drytown.
of Me Perry.
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137
GEOLOGY OF AMADOR COUNTY.
heated waters deposited their loads of silica, and, the ascending vapors their metalic deposit. From near Berranda, on the South Pacific Railroad, to Trinity on the north, spouting geysers and steam- ing solfataras, ladened the air with vapors, and marked the site of the gold deposits of to-day.
East of the Mother Lode, from one to three miles, a ridge of feldspathic rock runs parallel with the lode across the county. In some places, it is a com- pact granite; in others, a gncissoid granite. It is traversed in places by dikes of trap and large veins of barren quartz. At Quartz mountain, on the line of this granitic ridge, is an immense deposit of quartz, low grade ore. The auriferous slates of the county are arcnaceous, argillaceous, and quartzose, sometimes changing in a few rods, from magnesian to aluminous, or to hard, blue metamorphie slates. These slates further ehange as we go west, and at the Newton copper mine we find them an argillaceous shalc.
When excavations are made in the alum slates, a deposit of that mineral forms on the damp walls, and waters flowing from tunnels in the slates, arc sometimes heavily charged with alum from decom- posing pyrites of iron. These slates, as has been determined from fossils, found further north in Plu- mas county, belong to the upper triassic and jurassic epoch.
The auriferous slates on either side of the great Mother Lode are of the same age as the Jura Alps, and hence jurassic. They have a width of about thirty miles from east to west. Five miles from Jackson, on the Voleano road, we find these slates divided by an immense ridge of granite; and three miles east of the town of Volcano, the granite rocks commence and extend, with slight interruptions, to the summit of the great chain of the Sierras. All the country rock, between these granite ridges, which cross the county in a northerly direction, is occupied by the auriferous slates- except where the carboniferous limestone divides it. There are several strata or formations of the limestone which cross the county in the same general direction that the quartz veins do. These limestones mark the near shore-line of a carboniferous ocean, and are the work of the coral polyps that once existed on the golden shores of Amador. It is a well-known fact that the coral insect does not live and work at a greater depth than one hundred feet; and at the period when these limestones were formed, the land lay at the bottom of a shallow sea; or the rising Sierras shifted the receding shore-line continually to the west. Hence we find the greatest deposit of the limestones on the east of Volcano, where they have a width of three thousand feet. Between Valcano and Sutter, we find two narrow strata of limestone; and three or four miles to the west of Sutter, we find the last, or most western, strata of the carboniferous limestones.
These limestones do not contain a fossil of the 18
coral polyps, who built them; not even with the microscope can they be detected. The strata has been so metamorphosed and changed by pressure, as to destroy the form, and change its beautiful coral formations (as found in the limestones of the same age in Shasta county), into erystalline marble. This limestone is a white, crystalline, saccharoidal marble of fine and coarse texture, with veinings of oxide of iron and black oxide of manganese. It is traverscd, in many places, by heavy and light trap- dikes.
Previous to the deposition of the gold-bearing gravel upon it the rock has been worn by the action of the elements into the most fantastic shapes. By the removal of the auriferous gravel covering, the limestones, domes and spires, monuments and towers, of dark-veined marble have been exposed to view, presenting an imposing appearance. It is full of pot- holes formed by the action of water, and deep, curiously eroded cavities, once filled with gold-bear- ing gravel.
Caves, caverns, and long, sinuous galleries have been formed by the eroding waters carrying the car- bonate of lime in solution, depositing it at different parts of the deposit, in many instances decorating the roofs and floors of the caverns with beautiful stalagmite and stalactite formations. The lime- stone belt is erossed by quartz veins of small size. Layers of flint, or chert, possibly formed from the cast-off shells of diatoms, are found along the line of the marble and slaty beds of the same rock. The gravel deposits, which at Volcano have been exten- sively worked for gold, rest on the auriferous slates as well as the limestones. Beneath the limestones the slates are not found.
In the ridge north of the town (Volcano) the auriferous gravel is overlain by horizontal beds of white and pink tufa or voleanie materials, consisting of ashes and pumiee cemented and stratificd by water. Upon these horizontal strata rests a mass of trachyte, broken into rounded forms on the surface. Under this massive volcanic ridge, the entire aurifer- ous belt plunges, re-appearing on the opposite side, at Fort John.
Between the Volcano basin and the Mokelumne river is another high ridge of volcanic materials, under which the auriferous belt passes in a southerly direction.
These volcanie ridges-which may be met with all along the western slopes of the main ehain, extend- ing in parallel courses from the summits of the high Sierras to the low tertiary foot-hills, which in many instances they cap with a shallow deposit-extend in a continuous line to the summit of the Sierra Nevada.
These ridges push out in detached masses to the confines of the Sacramento valley, where, becoming thinner and thinner, they have finally stopped, and are found on the summits of the low tertiary hills around Ione valley.
138
HISTORY OF AMADOR COUNTY, CALIFORNIA.
Near the surface in some of these tufa deposits, may be found beautiful specimens of what are called photographic rock-dendritic formations; generally resembling delicate tracery of trees and shrubs.
Some of the pictures are ideal landscapes, with hill, valley, and lake; the lake in the foreground, bordered by grass and ferns, the low hills in the back- ground with palmate and branching trees, delicate as sca mosses. They are not, as supposed, nature's photographs, but are formed by waters, holding black oxide of manganese in solution, percolating through the fissures in the rock. These formations are abundant in the claims of Mclaughlin & Co., on Union Flat, and Whitney & Co., on the same range ncar Volcano.
The jurassic and carboniferous strata are overlain by the strata of the tertiary and post-pliocene, with boulder or glacial drift and aluvium deposits. The volcanic deposits cap the whole, and are consequently the latest formations.
GLACIAL EVIDENCES.
On the summits of many of the high ridges, both exposed and under the lava flow, arc deposits of glacier drift, in places rich in gold. The question with many is, how these immense polished boulders have been left on the summits.
The solution of the question is that they were carried there in the glacial period, after having been torn from the numerous quartz, and other ledges, over which the glacial flow passed, carrying them over valley and hill-as they are known to have traveled -from a northerly direction. The great body of ice, possibly two or three miles in thickness, acted as a mighty arastra, grinding down the quartz lodes, pulverizing the mass, polishing the boulders, and depositing the gold in the drift (to be concentrated afterwards by the flowing streams from the melting ice), wearing down the slates, and leaving the aurifer- ous gravel in the beds of the rivers and gulches, filling the great valley of the Sacramento to an unknown depth. The Stockton artesian well, sunk to a depth of eleven hundred feet, did not go through the deposit, nor the well at the Sacramento sugar refinery, two thousand two hundred fect in depth, the auger bringing up gold, quartz, and wood, at a depth of two thousand feet. We mention thesc deep sinkings in the valley to show that the debris, for countless ages, has been pouring into the valleys, and must for countless ages to come. Three miles west of the town of Amador we find evidences of glacial deposit. On the summit of one of the volcanic ridges, min- gled with the huge, rounded trachyte boulders, are fifteen granite glacier-polished boulders. The larg- est is thirteen feet long by seven and one-half feet wide; the part above ground is five feet high. It contains fifty tons of rock, and has the ovid or shcep-back form peculiar to glacial boulders. The others, all similar in appearance, are much smaller. There is no granite of the same character nearer
than twenty miles north-cast, in an air linc. Wo followed the line of the glacier drift over the vol- canic ridges, and down the deep cañons, to near Upper Rancheria, where we again came upon the same character of granite boulders, but distant from the first mentioned by ten or twelve miles. They are from five to thirty tons weight. They mark the line of the glacial flow, and their polished sides show the action of the moving icc.
VOLCANOES.
There are no well-defined volcanoes, with the cx- ceptions of Butte mountain, near Jackson, and one west of Tragedy Springs, near Silver lake. At the last-mentioned point, there are evidences of the most stupendous volcanic outbursts, and from this point the lava ridges may be traced for forty miles or more, toward the valley of the Sacramento. These lava rivers in the volcanic epoch, flowed down the lowest places, or river beds. As the ages rolled on, the eroding waters and high mountain glaciers, wore the softer slates away, and left these ridges, as we find them to-day, the most elevated portion of the county. That portion of the county to the east of the great Mother Lode, is traversed, to a greater or less extent, by igncous rocks, mostly trap and diorite. These dikes cut through all formations, and are found extending to the boulder drift and aluvium deposits. (According to Clarence King, United States geologist, they were erupted in the cretaceous, or chalk period.) They are from a few inches in width to many (sometimes five hun- dred) feet wide. We have traced many of them for a distance of two miles, through several formations. They are, in many instances, intimately connected with the formation of quartz lodes; and where they cut a ledge or intersect it, deposits of rich ore are often found. In the Pioneer district, five miles east of Volcano, the small quartz lodes in the granite, owe their origin to these trap-dikes; they are what is known as segregated lodes, that is, drawn from the granite by the heat of the ascending dike.
Trap-dikes cross the basin on which the town of Volcano is located, in almost all directions. The richest placer deposits have been found in close proximity to these erupted dikes, on one or the other side. They appear to have acted as gigantic riffles during the glacial period, and held the gold as it was ground out of the abundant quartz lodes, much as is common in a sluice at the present time. A large dike of doleritic trap rock, with large crys- tals of augite, malacolite, and sahlite, of a dingy green color, passes just above the falls on Indian gulch, near Volcano, and through which a tunnel has been driven. This heavy dike of igncous rock changed the inclosing limestones to a coarse crys- talline carbonate of lime, some of the crystals an inch square. Some very good marble has been formed in the same way, at various places on the limestone belt. This great dike, in a few hundred
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GEOLOGY OF AMADOR COUNTY.
feet, frays out into numerous small dikes; some of them cutting small quartz veins, in the here silicious limestones, which show gold where the trap passes through the quartz.
Butte mountain gives indubitable evidence of hav- ing been erupted on the spot, the molten matter coming up through an opening in the slates. We find the conical mountain composed of volcanic rocks and ashes, resting on the auriferous slates. This mountain is a conspicuous figure in the landscape, and the view from its summit, extensive and grand.
COPPER.
What is known as the copper belt, and on which the Newton copper mine is located, passes across the county five or six miles to the west of the great Mother Lode. The slates in this section are the magnesian and argillaceous. Large ledges and strata of serpentine rocks cross and cut these slates in all directions. The ore obtained at the Newton mine is the sulphuret, known as chaleopyrite, the yellow oxide of copper. There is some iron pyrites mixed with the ore to a greater or less extent, which lowers the percentage of the ore correspond- ingly; red oxide is also obtained in smaller quanti- ties.
The process of working is simple. The ore is roasted, then leached, and the copper precipitated with iron, or rather, collected on iron seraps.
Along this copper belt are numerous croppings and evidences of the existence of other deposits of copper, and the future prospector may yet uncover mines equal to the one described above.
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