These alternations of beds of coal, clay, and rock may be repeated many times, and are known as the "coal-measures"; and in some regions, as in South Wales and in Nova Scotia, the coal-measures attain a thickness of twelve or fourteen thousand feet, and enclose eighty or a hundred seams of coal, each with its under-clay, and separated from those above and below by beds of sandstone and shale.

In a passage, which is the continuation of that already cited, he writes: "(3) The microscopical structure and chemical composition of the beds of cannel coal and earthy bitumen, and of the more highly bituminous and carbonaceous shale, show them to have been of the nature of the fine vegetable mud which accumulates in the ponds and shallow lakes of modern swamps.

When the coal-forest area became slowly depressed, the waters must have spread over it, and have deposited their burden upon the surface of the bed of coal, in the form of layers, which are now converted into shale, or sandstone.

At the bottom of them all, near Petersburg, Sir Roderick found a shale of dried mud (to quote his own words), "so soft and incoherent that it is even used by sculptors for modelling, although it underlies the great mass of fossil-bearing Silurian rocks, and is, therefore, of the same age as the lower crystalline hard slates of North Wales.

We therefore entered the bed of the river to examine it, and found two seams of coalone five feet thick and the other about six feet thickbetween beds of sandstone and shale.

The rock of which it is formed appeared to belong to the coal formation, as thin seams of black shale were seen in the rocks of which the lower strata of the hill are composed; but the natives making their appearance, it was not considered prudent to remain geologizing among the cliffs.

At noon we attained the high tableland; crossed two scrubby valleys bounded by sandstone hills, in the first of which the black shale peculiar to the coal formation showed itself, with a slight dip to the south.

The brown-red earth, the great rocks and the little stones, masses of gravel, shale, schist, cobbles, fine sandall in one intermingled mass was slipping, sliding, rolling, tumbling, falling and fairly leaping down the side of Gold Hill.

"I'll get him!" Slipping, sliding, now being buried up to their knees in the soft mud and sand, again finding some harder ground, or shelf of shale, that offered good footing, Blake and the Spaniard struggled on through the rain.

A task that would have appeared impossible when viewed in daylight, lost half of its terrors because we only vaguely apprehended the dangers that threatened us when a layer of shale crumbled beneath our feet.

An' he'll travel mostly nights, layin' high up in the rocks an' shale during the day.

Their hoofs soon began to clatter on boulder and shale, and for another half-hour Langdon heard the hollow booming of the rocks loosened by their feet high up among the crags and peaks.

He was keeping to the high slopes where there were little dips and meadows, broken by patches of shale, deep coulees, and occasionally wild upheavals of rock.

For two hundred yards his progress was easy, and then the patch broke into a thousand individual tracks on a slope of soft and slippery shale, and it took him five minutes to make the next fifty yards.

It is a compound of aluminum and other matter, and, when mixed with carbon and transformed by the processes of geologic action, it becomes the shale rock which we know and which we discard as worthless slate.

In the manufacture of alum near Glasgow the shale and slate clay from the old coal pits constitute the material used, and in France alum is manufactured directly from the clay.

Taking a columnar section of our coal field, and computing the thickness of each shale stratum, we have from twenty-five to sixty feet in thickness of this metal-bearing substance, which averages over twenty-five per cent.

In a series of gigantic leaps, each longer than the last, it thundered downwards, at each jump starting fresh tons of the loose shale which covered the bank.

The gun, dismounted, was half buried in a pile of shale which lay feet deep across the road.

It was an awkward job to get down the bank, for the shale was so loose it kept breaking away under their feet.

"What is shale?" inquired Helen.

I jumped from rock to rock, and climbed over scaly ledges, and set tons of yellow shale into motion.

The slopes of the alluvial soil were dotted with little buttes of mingled sandstone and shale, varying from five to twenty feet in height, many of them bearing a grotesque likeness to artificial objects.

This time it burned suddenly clear and large and very bright, away off to the left of him where he had by daylight noticed a bare shale slide.

Casey kicked him gently with his heels to urge him forward, for in spite of what his reason told him about the shale slide his instinct was to go straight to the light.