The San Francisco call., 1898-01-23

ing carried out to work the beds of rivers reputed to be rich by construct ing head dams, by which the water is diverted into large fumes which carry 1t below the point at which it is de- signed to extract the gravel. This syS- tenn involves considerable expense, and is usually attended with great uncer- tainty as to the success of the enter prise.
 Dredges are used in a few localities where gravel occurs below the drain age level of the locality to elevate the gravel to a point sufficiently high to obtain the requisite grade for sluicing and for the dump.
 The gold-Saving apparatus of the shallow placer mine-the pan, cradle, tom, Sluice, etc.-are now objects of hardly more than historical interest. From their nature, as compared with the illimitable resources of the deep placers, the shallow diggings, as source of gold, will be but of a tran sient character The virtual exhaus- tion of the superficial gravel deposits gave origin to that prospecting" for the source of gold which resulted in the discovery of the deep placers and of the quartz veins.
 From these discoveries dates the in- aUguration of mining as scientific and permanent industry in this State.
 The quartz powders found in gravel mines often carry considerable. gold. At Polar Star mine, Dutch Flat, white quartz powder was found which contained $5760 worth of gold. The gold has undoubtedly been derived from the gold-bearing quartz veins so numerous along the western slope of the Sierras. By water it has been transported and deposited along with the detritus in preceXisting valleys, where now found. In the quartz veins the gold rarely. eX- of Iarc ciz off in the gravel deposits, and this would seem to be incompatible with the the ory of it's source as above given.
 Formation of Nuggets-To explain this seeming incongruity several the ories have been advanced. Professor Whitney is of the poinion that the gold veins were richer nearer the surface in pliocene times than now, and main- tains that gold veins get poorer as depth is attained. In the judgment of the writer, who has examined nearly all the mines of this State, there is no connection between the richness of the ore and the depth at which found. A more plausible explanation of the for nation of the nuggets is, as has been suggested by Le Conte and other geolo- gists, that their large size is often due to a chemical as well as a mechanical phenomenon. It seems probable that the gold has been redissolved and re- precipitated. By oxidation, the iron py- rites has been changed into the sul- phate. Percolating solutions of the sul- phate of iron dissolve the gold with which it comes in contact, and coming in contact later with organic and other reducing agencies, the sulphate of iron is changed by them to the sulphuret, depositing the gold as this change takes place By the deposition of gold in some such manner, from solutions con stantly in the same place, nuggets are formed.
 The aggregate length of the ancient channels has been estimated at 400 miles. This does not include the so- called cement channels, which are but of subordinate economic importance. The yield per mile of channels of the average character is, at a low estimate, from s2.0000e0 to s3,000. .000. Good chan nels for drifting yield from $100 to $500 per lineal foot of the stratum extract ed. From one-fifth to one-half of the gold in the channels usually may be ob- tained from drifting, where the bed rock gravel is accessible: the lowest stratum of gravel. four to eight feet in depth. carries this portion of the az gregate gold contents of the channel.
 Hundreds of millions have been taken out of the gold deposits of Cali fornia but her treasures of gold have hardly been touched.