The beds or 'seams' of coal vary in thickness from a thin film to several yards, and are separated from one another by layers of hard clays and flagstones. From the flagstone beds are obtained the square slabs with which the pavements of our towns and cities are laid. In many of the quarries near the Cheshire coal-field you may watch the workmen cutting and shaping these stones. The beds of clays and seams of coal make up what are called the 'Coal Measures'. These in their turn rest upon a foundation of hard rock, harder than any we have yet examined, called Millstone Grit or Gritstone. Boys who live in the hilly parts of East Cheshire are very familiar with it, for very probably the houses in which they live and the churches and chapels where they worship have been built of this stone. It is composed of coarse sand and grit, and, like the red sandstone, is a waterlaid deposit several thousand feet in thickness. The Pennine Hills, on the borderland of Cheshire and Derbyshire, are covered with Millstone Grit, which has been thrust upwards by the crumpling and arching of the rocks beneath it. Below the Gritstone are still older rocks of a different character called the Limestone series. The uppermost beds contain layers of a sandy substance called Yoredale sandstones. Mixed with them are layers of shale, a dark bluish grey clay that crumbles into thin fragments when crushed with the hand, and thin seams of limestone and, occasionally, of coal. These are the oldest rocks that are found anywhere in Cheshire. You may see them in the hills east of Macclesfield and Congleton and the higher parts of Longdendale. Below these beds is a mass of Mountain Limestone which has been forced upwards into an arch by tremendous pressure of rocks from either side, and has lifted up the Gritstone above to a height of nearly two thousand feet. In this way the highlands of East Cheshire, and indeed the whole of the Pennine Chain, have been formed. The Mountain Limestone, which consists almost entirely of animal remains, especially shells and corals, extends right under the highest hills of Cheshire, and comes to light in the cliffs of the beautiful dales of Derbyshire. Only at one spot, a quarry near Astbury, does it appear at the surface in Cheshire. The Coal Measures, Millstone Grit, Yoredale sandstones, and Mountain Limestone make up what geologists call the Carboniferous or Coal-bearing series, so called because in England our chief supplies of coal are obtained from this group of rocks.