lower down along the sluices. The first undercurrent was 790 feet distant from head of the sluice, and yielded 50 per cent. of the total yield of the undercurrents. The second undercurrent was 78 feet distant from the first, with a drop of 40 feet between them, and it contained 33 per cent. of the gross undercurrent yield. The third undercurrent was 91 feet distant from the second undercurrent, with a drop of 50 feet between them. Its yield was nearly $500.*

of a run.

It sometimes happens that a hundred or hundred and fifty feet at the head of a sluice are covered with gravel during the greater part In such cases, the gold is found so much further down the sluice. In the North Bloomfield tunnel, the upper 300 feet of the sluice is generally filled with gravel, from 1 to 5 feet deep, and still this portion yields much more amalgam per linear foot than the next 300 feet of sluice below.

From the report of this company for the year ending October 31st, 1876, the following data and facts are worthy of note, as showing the position of the gold as cleaned up in the sluices at No. 8 claim, where some 700,000 inches of water were run, washing 2,919,000 cubic yards of gravel:

THE DISTRIBUTION OF GOLD IN TAIL SLUICES.

The North Bloomfield tunnel (8000 feet in length) has 1800 feet of sluices, paved with blocks, at its upper end, but in the succeeding 6200 feet no sluices are used, the tailings being allowed to run on the bare bed-rock (a tough slate).

From the rock cut at the mouth of the tunnel a sluice paved with rocks receives the tailings. From here on they are carried through sluices and cuts, distributing them over undercurrents set on different grades, paved in some instances with rocks and blocks, and occasionally arranged with longitudinal riffles covered with strap iron. The grizzlies used are made of wrought iron one by four inches in size, set on edge.

*The figures showing the yield of the undercurrents were calculated from the amalgam.

The discharge from the several undercurrents is taken up by the main sluice, and subsequently redischarged over the succeeding undercurrents, till the lowest sluice and undercurrent finally discharge the tailings into the cañon. From December 1st, 1876, to June 1st, 1877, three hundred and fifty thousand (350,000) twenty-four hour miner's inches of water (2230 cubic feet each) conveying the tailings passed through the tunnel, and were discharged through the tail sluice and undercurrents.

The annexed sketch shows the general arrangement of the tail sluices and undercurrents, which latter were subdivided into compartments as shown.

The distribution of the gold along the line of sluices and in the several undercurrents was as follows:*

TAIL SLUICE, ETC., FROM DECEMBER 1ST, 1876, TO JUNE 1ST, 1877. Miner's inches of water, 24 hours each,

150 feet at head down to No. 1 undercurrent, yield, .

remainder of sluice,

Total,

850,000 $3150 00 350 00

$3500 00†

No. 1 Undercurrent.-Size, 24 by 36 feet; grade, 13 inches to 12 feet; chute, 2 feet wide at opening, contracted to 10 inches; iron rail riffles.

* I am indebted to Mr. H. C. Perkins, Superintendent N. B. G. M. Co., for the data given. The results show the total yield of the many places, the number of "clean ups" made being noted in each case.

† 700,000 miner's inches water were used in 1875-6; the yield was $1800.

No. 2 Undercurrent.-Size, 24 by 24 feet; grade, 12 inches to 12 feet; chute, upper end 2 feet, lower end 2 feet; iron rail riffles.

No. 3 Undercurrent.-Size, 24 by 36 feet; grade, 15 inches to 12 feet; chute, 21 feet upper end, 2 feet lower end; rock riffles.

No. 4 Undercurrent.-Size 20 by 36 feet; grade, 12 inches to 12 feet; rock riffles.

No. 5 Undercurrent (constructed in March).-150,000 miner's inches of water; size, 24 by 24 feet; grade, 12 inches to 12 feet; chute, 2 feet upper end, contracted to 2 feet lower end. Riffles, 1 by 4 inches lumber, covered with strap iron, rails 1 inch apart.

No. 6 Undercurrent.-Size, 24 by 36 feet; grade, 17 inches to 12 feet of rock riffles; chute, 2 feet upper end, 2 feet lower end. 150,000 miner's inches of water.

The total yield of the undercurrents and tail sluices for the period mentioned was $7872, whilst the total yield of the claims was $145,000.

The amalgam from the main sluice is worth from $7.50 to $8.50 per ounce troy, whereas that of the undercurrents varies from $6 to $6.20 per ounce troy.

The result of the undercurrents and tail sluice "clean ups," for the year 1876-7, was as follows:

This amount (3170 ounces) equals in value about seven per cent. of the total yield of the mine for this last fiscal year, during which period 595,500 miner's inches of water have been used extracting $291,116,9% gold.*

*The cost of melting and refining has been deducted from the amount given.

Comparing these final results with those of the previous year, 1875-6, the precious metal is found distributed throughout the sluices and undercurrents in the same relative proportion.

This fact is worthy of note since last year the bulk of the material moved was "top gravel," whilst this season a much larger proportion of cement gravel has been run through the sluices.

In the heavy cement at French Corral and Manzanita a high percentage of the gross yield of the mines is found in the undercurrents. Hydraulic mining in the so-called "cement claims" is carried on under great difficulties. An exhibit of the workings of the sluices of a representative cement claim (French Corral) is here given, and the contrast thus afforded with the workings of sluices in the generality of cases is most striking and especially interesting.

The washings from the French Corral Mine, after passing through the new tunnel, are distributed successively over nine undercurrents before they are finally discharged. The sizes and arrangement of these undercurrents are given in the accompanying table.

From January 14th, 1877, to October 3d, 1877, there were 163,263 miner's inches of water discharged over these undercurrents,

* Grade fifteen inches to fourteen feet.

Riffles, made in frames seven feet long, twenty inches wide, from slats 1 x 4", " apart. The bottoms of the undercurrents were lined with slat riffles, until clean up of July 21st.