The use of natural gas as fuel at steelworks and in rolling mills in the United States was for a time increasingly prevalent; in 1892, owing to a smaller supply, its use declined. In that year there were 74 mills wholly or partially depending upon this product, this being a reduction of 30 in two years, notwithstanding the development during that period of the gas-bearing region in the central part of Indiana, where several iron and steel industries have arisen. Bituminous coal, gas coal, and petroleum are used as substitutes at those works which have been obliged to abandon the use of natural gas. Fresh bores are continually being made in order, if possible, to maintain a gas supply.

From the bed of a diminutive river called the Cat Fish Run, in the petroleum regions of Pennsylvania, the natural gas rises in bubbles, which explode on the surface. Not many years ago, some visitors to the neighbourhood, by way of experiment, floated some burning rags down the stream towards the gas, which then ignited with an explosion. Other instances have occurred in which the gas has been lighted on the surface of the water at night, giving the magnificent appearance of a sea on fire.

Such a fire was observed in 1845 on a small scale on the river Wear, near the city of Durham, and from its singular appearance attracted much notice. The Durham Advertiser in August of that year relates that at certain points in the river near Framwellgate Bridge on perfectly calm days large numbers of air or gas bubbles issued from below as though the water were boiling. A gentleman in the neighbourhood, thinking that it might be due to the escape of light carburetted hydrogen through a fissure from a seam of coal under the bed of the river, determined to make an experiment. For this purpose, choosing a day when there was no wind, he moored a boat alongside the disturbed surface of the water and set fire to the gas. Subsequently a pipe with a bell-mouthed end was fixed over the supposed fissure in the river bed, and the gas collected and conveyed through it to a reservoir floating on the surface. The receptacle was provided with a burner and glass chimney. A brilliant jet of flame could then be commanded at pleasure. There were several other places beside the one at which the experiment was conducted, the total escape from which amounted to many cubic feet of gas per minute. In favourable weather these could be ignited by holding a light close to the water until the ascending gas came in contact with it. In the absence of wind, rain, &c., separate clusters of gas jets could thus be lighted on the water, the extreme clusters being distant about 100 yards from one another. This series of burning jets scattered about in irregular patches on the surface of the water when seen from the bridge at night looked like a burning river. No coal workings were known to exist within two miles which could cause a subsidence, and the occurrence was probably due to a large natural accumulation of firedamp at a fault, which extended to the surface with interstices at the lines of broken strata. In the neighbourhood of Baku, on the shores of the Caspian, gas issues from the ground in great abundance, and over large tracts, as though the soil were completely impregnated. The land glare of the fires by night is an amazing sight, as may well be imagined. In some instances, the flame is utilised for domestic purposes.

The analysis of the gas at Pittsburg is as follows:

Natural gas in the United Kingdom occurs only in limited quantities. That which is found in coal mines has been fully dealt with elsewhere in this work. Gas given off at the Wallsend Colliery was burned on the surface for several years, and in many other collieries, "blowers" of firedamp have been conveyed to the surface and used there. In two of the three series of experiments made with safety lamps in explosive mixtures by the Royal Commissioners on Accidents in Mines, 1886, two natural gases were made use of, one given off at a powerful blower at the Garswood Hall Colliery, near Wigan, and the other at the Llwynypia Colliery, South Wales. In the former case, the gas issued from the Wigan 9-foot seam which had just been reached in the newly sunk shaft, and was quite unworked at the time of the experiments; in the latter, the gas was obtained from the sandstone about 60 yards above the 6-foot seam of the Rhondda valley, and piped to the surface. Gas occurs in the jet rock of the Upper Lias in East Yorkshire, together with some heavy liquid bitumen; and it also finds its way down into the ironstone mines worked in the Middle Lias. A blower was burned for over 20 years in the Grag Hall ironstone mine, a few miles south-east of Saltburn. In some of the first borings for salt at Middlesborough, gas was found, and oil at Seaton Carew, both being, as it is believed, from the upper beds of magnesian limestone. A deep boring at Port Clarence was continued 150 feet below the salt, in order to prove the magnesian limestone. The limestone yielded traces of bitumen, and there was also a constant escape of gas, which contained 83.2 per cent. of hydro-carbons, and 168 per cent. of nitrogen. Gas was found afterwards at the same place in greater quantities under considerable pressure, together with some petroleum.

Petroleum has also been found at Worsley (near Wigan), and West Leigh in Lancashire, in Shropshire, in Derbyshire, in North Staffordshire, and in Lanarkshire, but never in sufficient quantities to justify its working. The latest discovery is that in Somersetshire.

In Scotland, the working of the bituminous shales of the coal-measures is a very important industry. The oil shales are found in calciferous sandstone measures situated between the carboniferous limestone measures and the old red sandstone. They occur in small basins in the centre of Scotland. The seams of shale vary in thickness and quality, and are usually won by mines commencing at the outcrops on the surface and following the seam to the full dip. The thick seams are worked by pillar and stall method, the thin ones by longwall. The small shale which passes through one-inch riddles is stowed underground. Fire-damp is given off in the shale mines, which, however, are worked with open lights.

On distillation the shales yield naphtha, sulphate of ammonia, and crude oil. The crude oil when treated in the refinery produces burning, lubricating, and paraffin oils.

It has been suggested that although the strata of the United Kingdom are as fossiliferous as other regions in which petroleum and gas are largely produced, the paleozoic strata have been subjected at various ages to repeated foldings and denudations, leaving exposed edges which have facilitated the escape of any gas or petroleum which might else have been retained.

In Europe, petroleum has been found in Germany, France, Italy, West Sweden, in Spain in small quantities, Austro-Hungary, Hungary, Roumania, and Moldavia. There are also several deposits in Russia, beside that of Baku, which is one of the largest and oldest known. The oil is here found nearly colourless in soft sandstones interstratified with impervious clays of different colours, and requires no purification before being burned in lamps. Out of 1,600 square miles of oilbearing territory, only about 5 square miles have been developed. Up to 1890, some 500 wells had been bored on that area, the deepest being about 850 feet, while the average depth is about 500.

The known oil-fields of the United States are situated chiefly in New York, Pennsylvania, Ohio, West Virginia, Kentucky, Tennessee, and California. Between 1860 and 1890, about 50,000 wells had been bored, some being 2,500 feet in depth, while the average was 1,500 feet. The bore-holes vary in size, but are usually from 3 to 4 inches in diameter. At the 1893 World's Fair at Chicago, the Exhibition authorities used petroleum exclusively for the boilers there. It was brought from oil-wells in Ohio and Indiana. The oil-fields of Canada are near Lake Erie, and also on the coast and near the Rocky Mountains. The most important of these are in the valley of the Mackenzie and Athabasca rivers, and, according to the report of the Senate of Canada about 1886, they constituted the largest petroleum field in the world. About 10,000 square miles of this petroleum territory has been marked out as a reserve to be constituted as a Crown domain. The whole area is quite undeveloped. In Mexico, there are large deposits which have not yet been extensively worked. Petroleum occurs in many of the West Indian Islands.

Turning to South America, Venezuela and Peru have very extensive oil-fields; although no great efforts have yet been made to develop them. Those of Peru are likely to be of great importance. Petroleum occurs also in the Argentine Republic, and is said to have been found in Bolivia and New Granada.

Oil-fields have been discovered in South Australia on the banks of the Coorang, a little to the north of Salt Creek, and in New South Wales.

In New Zealand, there are similar fields undeveloped near Poverty Bay, Auckland, and in the Taranaki district. The latter are interesting from the fact that the oil bubbles through the pulverised iron ore that forms the beach along the west coast.

In North Africa, petroleum has been found both in Egypt, and, according to report, in Algiers.

In South Africa, there are oil-fields in the Transvaal and in the Orange Frec State. Little is known of these as yet, and there is room for speculation as to the future of Africa as an oil-producing country.

The Persian oil-fields are situated in the valley of the river Karun, but little has been done to develop them.

In Burmah and India petroleum occurs, and may some day lead to the development of important industries there.

It is also stated to have been discovered in China, and is known in Sumatra, Java, Borneo, and other islands in the eastern seas.

Petroleum deposits have also been worked in Japan.

The oil-bearing regions of the world, therefore, are vast and practically inexhaustible, even apart from the theory of constant production. The use of paraffin, both in a crude state and greatly purified, has made enormous strides during the last few years for public and private illumination, and for fuel and manufactures. The application of mineral oil as a fuel for ocean-going vessels, locomotives, and stationary engines is likely to undergo extensive development.

CHAPTER XIV.

SURVEYING AND PLANNING.

General Use of Working Plans-Chaining Distances-Construction of the Spirit Level-Of the Levelling Staff-Method of Taking Levels-Ordnance Bench Marks-The Adjustments of the Spirit Level-Forms of Levelling Book-Mr. Wells's Hints on Levelling OperationsThe Miner's Dial-Davis's Improved Hedley Dial-The Hoffman Joint-Stanley's Improved Miner's Dial-Stanley's Tripod for Dials-The Reflecting Cup-Method of Needle Surveying - Vernier or "Fast" Needle Surveying-Reducing Angles to an Original Base Line-Stanley's Hanging Dial-Hanging Clinometer-Stanley's Mining Survey LampHenderson's Rapid Traverser-Declination, Diurnal Fluctuation, and Dip of the NeedleConstruction of the Transit Theodolite-Method of Using the Theodolite UndergroundThe Plain Theodolite-The Adjustments of the Theodolite-The Protractor and its UseThe Parallel Ruler and its Use —Scales—Ogle's Protractor—Survey Book-Paper for Colliery Plans-Meridianal Lines on Plans-Separate Plan of each Seam's WorkingsDesirability of Placing Full Information on Colliery Plans-Plotting the Surveys "Tieing Surveys Plotting Sections-Colouring Colliery Plans-Computation of Areas and Produce of Coal from them-Setting Out Railway Curves-Making Geological Sections-Louis's Improved Davis's Clinometer-The Celluloid Slide Rule-Practical Questions and Answers.

A VERY important item in colliery operations is the making and maintaining, in compliance with the Mines Act, 1887, accurate plans of the workings in the different seams.

Plans are indispensable as a guide to the mining engineer or colliery manager in directing the workings, designing the best means of ventilation, guarding against old workings containing water or gas, keeping well within and leaving a proper barrier against the boundaries defined in the lease of the colliery, and for giving notice to the proprietors of railways, canals, &c., when the workings have approached within a specified distance of their surface property. In some instances the royalty rents are chargeable on the amount of coal worked; such amount being calculated from the areas as proved by survey and plotted on the working plans.

Surveying instruments are divided into three classes:-1. Instruments for measuring distances. 2. Instruments for measuring angles. 3. Instruments for plotting the survey.

Those ordinarily used for Class No. 1 are the chain or tape, the spirit level and levelling staves. Those for measuring angles, which are applicable to mine surveys, are the miner's dial and the theodolite. Under the head of No. 3, the different forms of protractor, the parallel ruler, the T-square, the set-square, and scales, will be considered.

Gunter's Chain is that which is almost universally adopted for measuring distances. It is 66 feet or 4 poles in length, and is divided into 100 links joined together by rings. The length of each link together with the rings connecting it 66 × 12 with the next is = 7'92 inches. To every tenth link are attached pieces of brass of different shapes for readily counting the distances which may be fractional parts of a chain.

100

With the chain, on the surface, 10 or 11 arrows also are used, the latter number being preferable, but they are not often used in underground measuring as they will not stick in the floor, and the custom is to mark the end of a chain with chalk on the floor or the rails. Care is required to measure straight between the two marks set up, which on the surface are usually rods, and underground must be lights.

The best land chains are of steel, and made light and strong. Fig. 670 shows a land chain and arrows. The chain, whether made of steel or iron, has long links formed by turning up the ends of a length of wire. Three small oval links are placed between each pair of long links. Three interval links are found to cause the chain to kink less than when only two are used. Each oval link is sawn through at the meeting line, which is brought up on one flat side of the oval in bending it from the wire. The small links are used for the adjustment of the chain, as they may be closed to shorten, or forced open to lengthen it. There are generally four swivels in the length of the chain, two of which are at the handles: these prevent the chain from becoming twisted in turning the handles over in use.

The length of an ordinary measuring-chain is always tested, and, if necessary, adjusted by a standard chain before it is used in a survey of any importance.

Fig. 670.-LAND CHAIN AND ARROWS.

where the ground rises or falls.

Standard chains are of the same form as the ordinary steel chain, but all the links are hard-soldered after being adjusted link by link.

Standard chains are used at collieries only for testing and adjusting ordinary chains.

Horizontal distances only are shown on the plan, and these will not be the actual distances measured On the surface, approximate horizontal measurement may be obtained by holding one end of the chain up, so as to keep it in a horizontal position, and plumbing from the handle to the ground; but where the ground is very steep, it is impossible to hold out a whole chain-length in this way, and it has to be done by using a part of the chain, say 40, 30, or 20 links at a time, according to the fall of the ground. It is, however, difficult to tell when the chain is being held horizontally, and it is much better, instead of adopting this method, to measure the distances along the surface of the ground; and by taking the angles of elevation or depression over the several inclined parts of the line with the instrument used for measuring the angles, the correct horizontal distances may be computed. The underground measuring admits of no other method. Tables prepared from calculations may be obtained, showing this correction for every 100 links for any angle whatever. For measuring the depths of shafts, or in making plans whose areas are required in square feet, or it may be for plans of surface buildings or other purpose, a chain 100 feet in length, divided into links a foot long, is to be preferred. Chains made of steel are lighter to use than those made of iron.

The tape may be made of any length, but those mostly in use are 33, 50, 66, or 100 feet long, and there are different ways of dividing them. The most generally useful one is divided into feet and inches on one side and links on the other, so that it can be used to measure either. In surveying it is used to measure long offsets from the chain, the lengths of buildings, &c., on the surface, where its use is a necessity in addition to the chain, but it is seldom required in underground surveying. Tapes shrink in use, and should be frequently tested by standard measurement.

The Spirit-Level is an instrument used in measuring the vertical distances