out a twenty-four inch core from each of the great pillars, and thus relieved the danger.

In the most economical and successful stone drills compressed air is employed as the motive power to drive the drills, which may be used singly or in gangs, and which may be adjusted against the rock or quarry in any direction. When in position and ready for work a few moments will suffice to bore the holes, apply the explosive and blast the ledge. The cleaning away of submarine ledges in harbours, such as the great work at Hell Gate in the harbour of New York, has thus been effected.

Crushing:-Among the most useful inventions relating to stone working are machines for crushing stones and ores, and assorting them. The old way of hammering by hand was first succeeded by powerful stamp hammers worked by steam. Both methods of course are still followed, but they demand too great an expenditure of force and time.

About a third of a century ago, Eli Whitney Blake of New Haven, Connecticut, was a pioneer inventor of a new and most successful type of stone breaking machines, which ever since have been known as the "Blake Crusher." This crusher consists of two ponderous upright jaws, one fixed and the other movable, between which the stones or ores to be crushed are fed. Each of the jaws is lined with the hardest kind of chilled steel. The movable jaw is inclined from its lower end from the fixed jaw and at its upper end is pivoted to swing on a heavy round iron bar. The movable jaw is forced toward the fixed jaw by two opposite toggle levers set, in one form of the crusher, at their inner ends in steel bearings of a vertical vibrating, rocking lever, one of the toggles bearing at its outer end against the movable

jaw and the outer toggle against a solid frame-work. The rocking lever is operated through a crank by a steam engine, and as it is vibrated, the toggle joint forces the lever end of the movable jaw towards the fixed jaw with immense force, breaking the hardest stone like an eggshell.

The setting of the movable jaw at an incline enables the large stone to be first cracked, the movable jaw then opens, and as the stone falls lower between the more contracted jaws, it is broken finer, until it is finally crushed or pulverized and falls through at the bottom. The movable jaw is adjustable and can be set to crush stones to a certain size.

As the rock drill made a revolution in blasting and tunnelling, so the Blake crusher revolutionised the art of road making. "Road metal," as the supply of broken stones for roads is now called, is the fruit of the crusher. Hundreds of tons of stone per day can be crushed to just the size desired, and the machine may be moved from place to place where most convenient to use.

Other crushers have been invented, formed on the principle of abrasion. The stones, or ore, fall between two great revolving disks, having corrugated steel faces, which are set the desired distance apart, and between which the stones are crushed by the rubbing action. In this style of machine the principle of a gradual breaking from a coarse to a finer grade, is maintained by setting the disks farther apart at the centre where the stone enters, and nearer together at their peripheries where the broken stone is discharged. Large smooth or corrugated rollers, conical disks, concentric rollers armed with teeth of varying sizes, and yet so arranged as to preserve the feature of the narrowing throat at the bottom or place of discharge, have also been devised and extensively used.

A long line of inventions has appeared especially adapted to break up and separate coal into different sizes. To view the various monstrous heaps of assorted coals at the mouth of a coal mine creates an impression that some great witch had imposed on a poor victim the gigantic and seemingly impossible task of breaking and assorting a vast heap of coal into these separate piles within a certain time-a task which also seems to have been miraculously and successfully performed within such an exceedingly short time as to either satisfy or confuse the presiding evil genius.

Modern civilisation has been developed mostly from steam and coal, and they have been to each other as strong brothers, growing more and more mutually dependent to meet the demands made upon them.

The mining of coal, and its subsequent treatment for burning, before the invention of the steam engine, were long, painful, and laborious tasks, and the steam engine could never have had its modern wants supplied if its power had not been used to supplement, with a hundredfold increased effect, the labour of human hands.

It being impracticable to carry steam or the steam engine to the bottom of the mine for work there, compressed air is there employed, which is compressed by a steam engine up at the mouth. By this compressed air operated in a cylinder to drive a piston, and a connecting rod and a pick, a massive steel pick attached to the rod may be driven in any direction against the wall of coal at the rate of from ninety to one hundred and twenty blows per minute; and at the same time the discharged compressed, cold, pure, fresh air flows into and through the mine, affording ventilation when and where most needed.

In addition to these great drills, more recent inventors have brought out small machines for single operators, worked by the electric motor.

After the coal is lifted out, broken and assorted, it needs to be washed free of the adhering dust and dirt; and for this purpose machines are provided, as well as for screening, loading and weighing. The operations of breaking, assorting and washing are often combined in one machine, while an intermediate hand process for separating the pieces of slate from the coal may be employed; but additional automatic means for separating the coal and slate are provided, consisting in forcing with great power water through the coal as it falls into a chamber, which carries the lighter slate to the top of the chamber, where it is at once drawn off.

The chief of machines with ores is the ore mill, which not only breaks up the ore but grinds or pulverises it.

Some chemical and other processes for reducing ores have been referred to in the Chapter on Metallurgy.

Other mechanical processes consist of separators of various descriptions-a prominent one of which acts on the principal of centrifugal force. The crushed material from a spout being led to the centre of a rapidly rotating disk is thrown off by centrifugal force; and as the lighter portions are thrown farther from the disk, and the heavier portions nearer to the same, the material is automatically assorted as to size and weight. As the disk revolves these assorted portions fall through properly graded apertures into separate channels of a circular trough, from whence they are swept out by brushes secured to a support revolving with the disk.

Many forms of ore washing machines have been invented to treat the ore after it has been reduced to powder. These are known by various names, as jiggers, rifflers, concentrators, washing frames, etc. A stream of water is directed on, into, and through the mass of pulverised ore and dirt, the dirt and kindred materials, lighter than the ore, are raised and floated towards the top of the receptacle and carried away, while the ore settles.

This operation is frequently carried on in connection with amalgamated surfaces over which the metal is passed to still further attract and concentrate the ore. An endless apron travelling over cylinders is sometimes employed, composed of slats the surface of each of which is coated with an amalgam, and on this belt the powdered ore is spread thinly and carried forward. The vibrations of the belt tend to shake and distribute the ore particles, the amalgam attracts them, the refuse is thrown off as the belt passes down over the cylinder, while the ore particles are retained and brushed off into a proper receptacle. Amalgamators themselves form a large class of inventions. They are known as electric, lead, mercury, plate, vacuum, vapour, etc.

By the help of these and a vast number of other kindred inventions, the business of mining in all its branches has been revolutionised and transformed, even within the last half century. With the vast increase in the output of coal, and of ores, and the incalculable saving of hand labour, the number of operators has been increased in the same proportion, their wages increased, their hours of labour shortened, and their comforts multiplied in variety and quantity, with a diminished cost. The whole business of mining has been raised from ceaseless