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Most engineers will agree fairly well in regard to the quantities of developed ore and of probable ore in any mine, but great differences are to be expected in estimates of possible ore, which, of necessity, are forced predictions of the future based upon insufficient data. A reasonable method by which to evade such predictions is suggested by Mr. J. H. Curie; it is to purchase mines on the basis of the ore reserves plus a royalty for all the ore afterward discovered.

The cost of mining and treatment is a factor as important as grade of the ore, and is probably more subject to the personal equation than any other branch of an examining engineer's work: individual judgment based on experience is the final guide in an estimate of costs. This subject, which applies rather to the examination of developed mines than to prospects, is most thoroughly gone into in Mr. J. R. Finlay's book on "The Cost of Mining."

The relation between the width of a vein and the stoping width necessary to extract the ore, should receive careful attention in the examination of narrow veins. The minimum stoping width for machine drills is usually from 4 to 5 ft. ; ihe new air-hammer drills require less. For hand drilling, 30 in., or sometimes even less, is required.

The treatment accorded abnormally high assays will var\' with each property examined and with every engineer. The usual procedure is to reassay the sample one or more times, to determine if the high result is due to a rich speck in the pulp taken for assay. If the sample as a whole is found to be high, the cut should be resampled.

The best safeguard against salting is to decide upon a plan for safeguarding samples and never to make any exception in carrying it out, whatever the circumstances; if an engineer trusts his judgment as to whether he is in safe company, his judgment is almost certain to be at fault at some time during his career, but if he always maintains the same vigilance he will never be salted. Salting is the result of carelessness, and is inexcusable.

The interval between samples depends upon the regularity with which the valuable minerals are distributed. One extreme might be considered an absolute uniform mass, of whicli one sample would suffice, anc the other extreme, a segregation of all the valuable minera' into a single mass; it is therefore apparent that the propei interval between samples wil differ with each exposure sampled.

Samples should be accurately referred to some permanent object, such as a cross-cut, winze, or survey station. The intervals between samples should be measured along the center of the drift, as they otherwise will differ widely according as they are measured on one side of the drift or the other, and will therefore fail to plot correctly on the map.

Durable tags carrying the number of the sample should be inserted in each sack; some engineers use metal tags, some wood, but the usual practice is to use tough paper rolled up tightly to prevent abrasion. The following sample tag is excellent, and should be made up in books containing 50 sheets and numbered before going into the mine. The lower part of the tag is torn off, and after being rolled up, is inserted in the sack with the sample. Tearing the detached slip in half gives two numbers for the duplicates when the sample is cut down.

A discussion of sampling, although fully treated elsewhere, cannot logically be omitted; inasmuch as proper sampling is often neglected, the subject will bear repetition.

Sampling is expensive work if properly carried out, and no other kind of sampling is of any value.

The ideal sample is a uniform groove, or channel, across the full width of the ore, and no more; how closely this may be approached in practice will depend upon the material sampled and upon the time and care given to the work.

A mine that has beendressed for examination may be described as a trap for the examiningengineer. The favorable features are accentuated, andthe unfavorable developments are concealed,—drifts are walledup, or are allowed, or encouraged, to cave, winzes are allowed to fillwith water, and workings through poor stretches of the depositare tightly timbered to hinder examination. In stoping operationsbarren material is removed up to the best showings, whichare left undisturbed, on the supposition that the engineer willassume that the material stoped was payable ore.