the workings that passes immediately above it. One method of proving his work as he proceeds is as follows:-Suppose he has surveyed the adit level, and there are four winzes communicating with the 10 fathom level, and he has taken the bearing, and depression, and length of those winzes, and plotted or laid down this level and the true base of those winzes on his working plan. He then proceeds to survey the 10 fathom level, making good every thing as he proceeds; and of course when he arrives at the foot of those winzes which he surveyed in the adit, he minutely enters in his dialling book the mark at their foot, where he took his diagonal observation and measurement. Then in laying down his 10 fathom level, if all his work has been well done, the points in those winzes will exactly correspond with his survey in the 10 fathom level and on the plan, and this desirable check he may and should pursue throughout the whole survey. It is too common in these cases, in order to avoid the time and labor in surveying the winzes to "let them take their chance," by merely entering their "brace" in one level and "foot" in another, and let the truth of their respective bearings and underlay depend on the horizontal survey of the levels. This practice is reprehensible, and should never be tolerated. But, with all this precaution, we advise, by all means, that every part of the plan be proved by trigonometrical computation, and the surveys by fore and back diallings. Let us suppose we have surveyed a level by double diallings. How shall we ascertain if there is a perfect correspondence? We have introduced a problem on this subject, and it is plain that the final two sums of the traverse will demonstrate either the agreement or the difference. This being done, and the underground work proved correct, we proceed to construct or draw the level on the plan, and it is most desirable that we should know if this part of the work has been well executed; as we have computed the workings, we are furnished with a ready and certain test. Suppose we found, by computation, that the level gave, from beginning to end, 184 fathoms 3 feet of southing, and 34 fathoms 4 feet of westing. Now, applying these numbers to the plan, we shall, by the convenient help of the cardinal lines and instruments, presently prove if the latitude and longitude between the start and terminus of the level on the plan make good these lines. Lastly, I would recommend that the instru ments for drawing and keeping up the working plan should be a

6 or 7 inch circular protractor, on the best principle, with double limb and vernier scale for reading off the angle, so that there may be no guessing, or judging by the eye, merely, for the fractional part of the degree; also, a parallel ruler of the best kind I prefer those rulers that travel on rollers, both for expedition and accuracy, but I admit it requires some practice to use them well. There is an advantage in those rulers, in that they have an ivory edge and a graduated scale, so that the lengths may be pointed off at the same time that the line is drawn, without using a compass or dividers; and these two instruments are all that are required for the drawing department. The parallel ruler should be a foot long, divided into thirty feet to an inch; so that any line within the extent of 360 feet can be pointed off at once.

THE PRACTICAL MINER'S GUIDE.

PART III.

INTRODUCTION.

THE qualifications necessary to constitute an accomplished miner are more numerous and difficult of attainment than is generally imagined, even by persons deeply interested in mining affairs; and although it may not be expected that every one who fills a mining situation should be an adept in all the various branches of the art, yet it is certainly highly desirable that agents, who have the management of large adventures, should possess a general knowledge of every thing connected with the profession of a miner.

The following miscellaneous subjects are essential to the practical miner, and require no comment to set forth their utility; they may also be found useful and interesting to persons not immediately engaged in mining pursuits.

The first article consists in a description of the art of assaying silver; and as this has hitherto been a secret in the possession of but few persons, it is expected that it will form an acceptable part of the work, especially as it will come abroad at a time, when foreign mining speculations (where the seat of action is principally among the precious metals) abound beyond all precedent.

The next part of the work contains a plain statement of the method of assaying copper, including the established process of one of the most experienced and respectable copper-assayers in the county of Cornwall.-Rules for assaying lead and tin follow in succession, and this part of the treatise concluded with a description of the manner of extracting silver from copper ore, or of dis

covering the quantity of silver it contains; and probably this article also may be productive of beneficial effects to the mining interest, as there is great reason to believe that a considerable proportion of silver is contained in the ores produced from many of our copper mines. The method is very simple, and the trial may be quickly and satisfactorily made.

The subsequent part of the work is described in the table of contents.