When the lode is very flat, as at the Cornish mines of Wheal Jane and Wheal Kitty, the section is made along the lode.

*

30

20

ADIT

Fig. 91.-Transverse Section.

In this way a true idea is given of the ground worked; but an erroneous one with regard to depth. This method of projecting the section is necessary to enable the ground stoped away to be shown, as when the lode is so very flat, the back of one level in a vertical section would touch the floor of the next. As a rule, lodes are so vertical that a perpendicular plane may be taken for the section.

The workings of a metalliferous mine are represented in Figs. 90, 91, on a scale of about 20 fathoms to the inch. The mine has an adit-level and below that, 10-, 20-, 30-, 40-, and 50-fathom levels. The adit is north of the shaft. The engine shaft contains the pumps which lift the water from the sump or lowest point of the shaft to the adit-level, which comes out to the surface on the adjacent hill side. This shaft was sunk vertically to intersect the lode at the 10-fathom level, a cross-cut being driven to the adit. Then, instead of continuing vertically, necessitating the driving of cross-cuts to the lode, the shaft follows the latter. The shaded portions shown in the longitudinal section represent the projection of the ore masses, removed by stoping. In practice, such portions are not shaded but coloured-purple for tin, green for copper, blue for lead, &c. Between the 10- and 20-fathom levels a mistake arose, the winze and rise did not meet owing to an error of the dialler.

It will be found advisable to colour all the levels on one lode the same tint. Formerly it was the general practice to colour each level a different colour, the adit-level being blue, and

the levels below it red, green, yellow, violet, and brown in succession.

No scale is prescribed by law for the plans of the British metalliferous mines. The variety of scales used presents great difficulties with regard to the comparison of the plans of different neighbouring mines. In many districts, the plans are prepared in a slovenly and unsatisfactory manner. This is notably the case in the Derbyshire lead mines. There, according to Mr. A. H. Stokes, H.M. Inspector of Mines for that district, the majority of the mines have no plans whatever. Even at the larger mines which have plans, they are very roughly drawn and rarely indicate the extent to which the ore has been worked. The variable width of the levels is not shown, the latter being represented by a coloured line. The position of the best and most profitable parts of the mine, that is, the width to which the ore has been extracted, is shown as an ordinary narrow heading. In fact, the plans are not true representations of the mine, but merely represent the length of underground tramways. Sections of the mine are seldom made.

(b.) Colliery Plans. By the Coal Mines Regulation Act, 1887, the owner, agent, or manager of every colliery is compelled to keep, in the office at the mine, an accurate plan of the workings of the mine up to a date not more than three months previously, and the general direction and rate of dip of the strata, together with a section of the strata sunk through, or if that be not reasonably practicable, a statement of the depth of the shaft, with a section of the seam. Every such plan must be on a scale not less than that of the Ordnance Survey of 25 inches to the mile.

Representing collieries on a plan is a much more simple operation than representing metalliferous mines. The workings are projected on a horizontal plane. The coal withdrawn is coloured dark, and the direction of the air-current indicated by arrows. The intake air-current is coloured blue, and the return air-current red. The water-courses may be coloured green, drowned waste also green, and faults bright red shaded off on the dip. Main doors may be indicated by a D in blue, main stoppings by blue lines, and caution-boards by a C in red. The heights of the different points above the level of the shaft-bottom should be shown in red figures, and those below the level of the shaft-bottom in blue. The signs shown in Fig. 92 are employed on colliery plans.

When two or more seams are worked one above the other, and are shown on the same plan, they are distinguished by means of colour.

Admirable illustrations of the manner in which colliery plans should be executed are afforded by the plans which accompany the annual reports of H.M. Inspectors of Mines.

Surface Plans. The surface plan of a colliery or metalliferous mine requires great distinctness of detail. If the scale of about 25 inches to the mile is adopted, the conventional signs used on the maps of the Ordnance Survey should be employed. If the scale is larger, care must be taken to give the conventional signs such dimensions as will accord with the scale of the plan. Buildings are coloured crimson lake for houses, and dark grey (a light wash of indian ink) for outbuildings. The mine buildings may be distinguished from other buildings shown on the plan by having a darker tint of red. In representing objects on the plan, their natural colours are sometimes adhered to; in other cases a conventional colour is used. Thus, for grass land, a flat

tint of green (Hooker's No. 1) is employed; it is made of gamboge and indigo. Cultivated land is represented by a flat tint of burnt sienna. Adjoining fields are slightly varied in tint, furrows sometimes being indicated by coloured strips. Lakes and rivers are coloured light blue (cobalt), with a darker tint on each side. Marshes are represented by the blue of water, with horizontal spots of grass green. Roads are coloured with a light wash of burnt sienna, or yellow ochre. Hedges are represented by green dots for bushes, brick walls by a red line, and wooden fences by lines of a neutral tint. In large scale plans, the Cornish hedge, some 6 feet in width, is shown by two lines the true distance apart, with a wash of neutral tint along each side. In all cases the shadow is put in. The boundaries of the mine concession are indicated by strips of colour.

When the underground workings are drawn on the surfaceplan, in the latter there should be no more colouring than necessary. It will be found sufficient to colour the roads, buildings,

and water.

(c.) American Colliery Plans.-In Pennsylvania the law requires all anthracite colliery owners to prepare maps of all workings on a scale of 100 feet to an inch for the use of the mine-inspector. This scale is rather too large for convenient use, and consequently most of the working maps used for reference are constructed on a scale of 200 or 300 feet to the inch. These maps generally show all the important surface features, buildings, streams, roads, and railways, as well as the underground workings. The latter are commonly drawn in blue, red, or green ink. When several beds are worked, the workings are shown by different colours— a device especially necessary when the workings on one seam are above or below those opened on another bed. In addition to the general map showing all the workings, separate maps showing the workings on each seam are usually made. The survey-lines are plotted with a vernier-protractor, or a protractor of very large size, and the results checked by latitude and departure calculations. Tracings or blue-prints of the workings are supplied from time to time to the viewer. When not in use the plans are stored in large fire-proof vaults. The survey-notes are copied into office record books for future reference. With the exception of the work done by the U.S. Coast Survey, no other surveys in America can compare in accuracy with those of the anthracite mines.

The sharp foldings of the carboniferous strata of the anthracite region of Pennsylvania, have made the study of the structural geology of that region one encompassed with great difficulties. The necessity of having some definite information