T he author, in proof of the various internal movements in the crust of the earth, which formed the subject of his communication, referred to many well-known phenomena, such as the thin, soft, clayey layers always found between the various beds in our coal-pits, and which are composed of the ground materials of the contiguous beds—the soft fire-clay at the bottom, and sometimes forming the roof of our coal seams—the vertical cracks in all hard beds of coal and rocks, of which there are two lines running nearly at right angles to each other, one of which, running north-east and south-west, forms what in coal-workings is called the plane of the coal, the other, north-west and south-east, forming the so-called end cracks —also, the oblique cracks in softer strata, and the highly-polished surfaces so abundantly found in fire-clay, coals, &c., known by the name of slickensides. Fire-clay, especially when affected by the movements he referred to, was the worst possible roof that a coal-mine could have, and also the most dangerous, as it falls without giving warning. The finest seam of coal for domestic purposes in the Glasgow district has this kind of roof, which makes it very expensive to work; and large portions of the splint coal in the Wishaw district are all but unworkable, from their having this roof full of what the miners call “lypes” and “lunkers.” The author stated his conviction that, but for the movements he referred to, colliery managers would not require to leave such large