It is therefore only near the outcrop, or where the mine is not deep, that a fall in it disturbs the earth at the surface. But in the mining of the upper veins such disturbances were frequent. In passing through the coal regions one will occasionally see a depression, or a series of depressions, in the earth’s surface to which his attention will be attracted on account of their peculiar shape. They are not often more than ten or fifteen feet in depth, and though of irregular outline their approximate diameter seldom exceeds sixty feet. They are the surface indications of a fall in shallow mines, and are known as “caves” or “cave holes.” A section of country one or more acres in extent may, however, be so strewn with them as to make the land practically valueless. When the upper vein in the Wyoming region was being mined, buildings on the surface were occasionally disturbed by these falls, but not often. If houses had been erected over a shallow mine before the coal was taken out, strong pillars were left under them to support the roof, and if the mining had already been done and the pillars robbed, no one would risk the erection of a building over a place liable to fall, for these places were known, and points above them on the surface could be definitely located. Sensational stories are sometimes started concerning a mining town or city that it is liable any night, while its inhabitants are asleep, to be engulfed in the depths of some mine, the vast cavities of which are spread out beneath it. It is almost unnecessary to say that such dangers are purely imaginary. There is probably not a town or city in the mining districts so located that a single stone of it in the populated portion would be disturbed by a fall in the mines underneath it, supposing there were mines underneath it, and that a fall is liable to take place in them. The areas of surface which could possibly be disturbed by a fall are too limited in extent, and are too well known, to make such a general catastrophe at all within the possibilities. The mines in the upper coal seams have for the most part been worked out and abandoned long ago, and the roof rock has settled into permanent position and rigidity. In the deep mines of the present day no fall, however extensive, could be felt at the surface. The broken masses of roof rock that come down first would have filled up the cavities and supported the strata above them, long before any perceptible movement could have reached the surface. The conditions that lead to surface falls in the Middle and Southern regions are somewhat different from those that prevail in the Wyoming field. In the first-mentioned districts steep-pitching coal seams are the rule, and they all come to the surface in lines of outcrop. In driving breasts up from the gangway of the first level, it is intended to leave from ten to twelve yards of coal between the face of the breast and the outcrop; while over the outcrop will be from twelve