At Dutch Flat, in Nevada County, the duty of the miner's inch has been estimated * at certain mines to be as follows:

In the State Engineer's report the estimates are undoubtedly the results obtained after careful investigation of the subject; but, unfortunately, the quantity of water, grades and size of the sluices, and character of the riffles are not given.

According to Le Conte,+ "if the surface of the obstacle is constant, the force of running water varies as the square of the velocity, the transporting power of a current varying as the sixth power of the velocity; but the power of removing material will vary between the square of the velocity and the sixth power of the velocity."

The transporting power (as used by Le Conte) and the transporting capacity are terms which must not be confounded. Transporting capacity denotes the amount of material which running water carries along per unit of time.

The transporting capacity of sluices is generally great, er (comparatively) than that of rivers, on account of the usually heavier grades (from 200 to 300 feet per mile), regularity of cross sections, and character of the bottom and sides of the former.

In sluices where the riffles are blocks a larger amount of material is moved than where rock riffles only are employed. An increase in the grade of a sluice would necessarily increase its carrying capacity.

* By the State Engineer, W. H. Hall. State of Cal. vs. Gold Run Ditch and Mining Co. + "Elements of Geology," Jos. Le Conte, pp. 19, 20.

The dirt as it enters the sluice has its lighter portion taken up and carried in suspension by the current, whilst the coarse and heavy material moves along on, and in part above, the riffles, but below the surface of the water. Boulders and rocks move down the sluices with varying velocities and in different directions as they advance, aiding in stirring and disintegrating the cement gravel and earthy stuff, which little by little fall to pieces and into particles that, segregated as light material, rise towards the surface of the water. The rocks and boulders travelling over the riffles assist in keeping the material thoroughly agitated in the sluices, where it is alternately changing position from the bottom to the top, until it is finally discharged.

The material, wearing down as it advances, is kept from packing by the presence of the rolling rocks which still maintain their solidity. Light, sandy gravel requires very wide and shallow sluices, as it cannot be washed advantageously in deep sluices, unless by a proper mixture of rocks, which permits the use of a greater quantity of water, so that the capacity of the same sluice is increased.

A heavy grade will compensate for a limited supply of water. With an abundant supply of water and material, the capacity of sluices will depend upon :

Ist. The character of the material washed;

2d. The size and minimum grade of the sluices;

3d. The character of the riffles used.

The statement of some engineers that the transporting power (meaning capacity) of a sluice increases with the third power of its grade is not verified by the comparative tests which have been recorded. However, these tests, which give the only reliable data extant, were not made with the same material, so there is still a very important factor undetermined.

The empirical results thus far obtained demonstrate that the transporting capacity of a sluice set on a 2.08 per cent. grade, and that of a sluice on a 41⁄2 per cent. grade,

vary as the 1.52 to the 1.87 powers of these grades. How this will agree with the results obtained from properly conducted experiments on increasing from 4 or 4% to 8 or 9 per cent. grades remains to be ascertained. Mr. Hamilton Smith, Jr., considers that under these circumstances the transporting power (capacity) of the sluice will increase about with the square of the inclination.

Mr. P. M. Randall says that the transporting power (capacity) of water is as the 3.75 power of the velocity.

From official data of the Blue Tent Company of the amounts of light material washed on a 10% per cent. grade, it would appear that the transporting capacity for such material varies as the 1.20 power of the grade.

The time, means, and facilities for the careful and thorough investigation and determination of the duty of the miner's inch have not as yet been afforded to the engineers who have been appointed for this purpose. In most cases the amounts of material estimated to have been removed may be considered as mere approximations, as is evidenced by the wide differences in the many estimates which are given in the various publications.

In the suit of the State of California vs. the Gold Run Ditch and Mining Company the estimates of the amounts of material washed and remaining, made by the various engineers who had investigated the subject, showed differences as great as 33 per cent. where the question of size of excavations and cubic contents was alone at issue. The difference arose largely from attempts to reconstruct from insufficient data the former topography of the land mined, no accurate information upon the point being obtainable.

The only known attempts at any extended and detailed. investigation of the duty of the miner's inch have been made by the North Bloomfield and the La Grange Hydraulic Mining Companies. The results of the work performed at these mines are given in the annexed tabulated

statement:

CHAPTER XX.

STATISTICS OF THE COSTS OF WORKING AND THE YIELD OF GRAVEL.

CORRECT statistics showing the costs, the quantity of material washed, and the corresponding yield of gold are rare and difficult to obtain. In the early days of placermining in California the question to be solved by the miner was not what the gravel would yield per cubic yard, and what it would cost to move it, but rather how many ounces of gold-dust he could "pan out" or "rock out" between sunrise and sunset. What the miner required was that the daily yield in dust should exceed the cost of living, etc. When it fell below this he moved his camp to other grounds.

The wonderful productiveness of the river bars and shallow placers, attested by the gold bullion and dust shipments, created an extravagance usual to all new and rich mining countries, the baneful effects of which are still felt.

As the richest and most easily worked placers became exhausted the increasing necessity of mining on an extensive scale and with ample capital led to the formation of large companies. Then became evident the importance of determining beforehand the amount of gold in the various claims and the costs of working them. This last included various engineering problems, as the best grades, the duty of the inch, etc. In this manner the first data concerning the yield (commonly estimated per cubic yard, but very often, for the sake of convenience, per inch of water) of the auriferous gravels were published. Many