A wise coal operator never begins to open a mine for the purpose of taking out coal until he knows the character of the bed and the quality of the mineral. This knowledge can only be obtained by an exhaustive search for, and a careful examination of, all surface indications, and by drilling or boring holes down to and through the strata of coal. This is called “prospecting.” The examiner in a new field will first look for outcrops. He will follow up the valleys and inspect the ledges and the banks of streams. If he be so fortunate as to find an exposure of the coal seams, or of any one of them, he will measure its thickness, will calculate its dip and strike, and will follow its outcrop. He will also study and make careful note of the rock strata with which it is associated, for by this means he may be able to determine the probability of other seams lying above or below it. This examination of the rock strata he will make, whether coal is visible or not visible. It will be of much service to him. For instance, it is known that the great Baltimore vein in the Wyoming valley is usually overlaid by a coarse red sandstone. If the examiner finds rock of this character in that section, he has good reason to hope that coal lies beneath it. Under the lowest coal seam of the anthracite beds there is found, as a rule, a rock known as the conglomerate. If, therefore, the explorer finds an outcrop of conglomerate, he will know that, as a rule, he need not look for coal beyond it. This rock, coming to the surface on the westerly side of the Moosic range of mountains, marks the limit of the Lackawanna coal field toward the east. No one, having once studied the conglomerate rock, could mistake it for any other, though its composition is very simple. It is nothing more than white, water-worn quartz pebbles, held together by a firm, lead-colored cement. But it is a rock of unusual hardness and durability. It is proof against the erosive action of water, grows harder by exposure to the air, and has a consistency that approximates to that of iron. In the coal districts it is used largely for building purposes, where heavy walls and foundations are required. Experience has taught that there are no coal seams below the conglomerate, so that wherever this is found as a surface rock, or wherever it is pierced by the drill, it is usually unnecessary to explore below it. If no coal outcrop is found, the bed of a stream is searched for fragments of the mineral, and, if any are discovered, they are traced to their source. Coal is sometimes exposed where a tree has been uprooted by the wind, and pieces of it have been found in the soil thrown out at a groundhog’s burrow.