BRADLEY COAL-MINE.

141

"though it only extends over an area of about sixty square miles, is very productive, from the great thickness of the coal-seams, or beds. In this Bradley Colliery, the upper beds of coal, which are called the flying reed, are separate from the rest, for beds of slate or slate-clay, and iron-stone are interposed between them. These upper beds, which are distinguished as the roof, the floor, and the top slipper, crop out; while the main body of the coal, which is only eight yards thick, goes on to Bilston."

"Only eight yards!" cried James, "why that is twenty-four feet!"

66

The greater part of the beds in this district consist of what is called ten-yard coal; and in many places the thickness of the coalseam exceeds forty-five feet."

"Is any of this coal sent to London ?"

66

Very little. It is principally used in the

142

BRADLEY COAL-MINE.

numerous iron-works in the neighbourhood, and in the manufactories of Birmingham and the adjacent towns."

They now examined the mode of working the mines; they saw the men breaking the coal with pickaxes, and by driving wedges into the rock; and as the pieces of coal were detached, they were placed in buckets, called skips, and as each skip wsa loaded, it was conveyed on a little waggon to the bottom of the shaft, up which it was drawn by the same rope and pulley which had served Mr. Thompson and his son as a means of descent.

The small coal, or slack, was in the meantime collected by another of the colliers, and drawn up in separate skips.

When Mr. Thompson and his son left the mine, they noticed the difference between the stone-coal of South Staffordshire, and the cak

FAULT IN COAL-MINES.

ing-coal of Newcastle and Durham.

143

"The stone

coal, or splint-coal, as it is sometimes called from its splintering fracture, contains less bitumen, and more earthy matter than the Newcastle coal, and consequently yields a larger quantity of ashes when it is burnt. There are also numerous faults in the Dudley Coalfield."

"What is a fault?" asked James.

"Coal is generally

found in slightly in

clined strata, alternat

ing with beds of sand

stone, slate, and clay;

but sometimes the coal- Vertical section of inclined coal measures. measures, as they are called, appear to have cracked across, and the fissure to have been filled up with clay. This is called a fault or dyke. Sometimes the coal-measures, with their

intervening strata, appear to have been violently tilted up, and a new stratification to have commenced on them. This is called unconformable stratification. And sometimes the coal-measures are broken into several levels, and intersected

in the level of the strata on both sides of it, and occasionally they are still more numerous."

"I suppose," said James, "that the dykes lessen the value of the mines."

"Sometimes," replied his father, "they are mere rents, which, when filled with stiff clay, are useful in preventing water from penetrating through all the coal-measures, when it has en

Coal-measures intersected by numerous dykes.

tered into one part of the mine; but occasionally they have a contrary effect, and serve as conduits for springs, so that when they are accidentally broken into, they cause such a flow of

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