Up to the present time timber has been used in underground-operations to the almost total exclusion of all other materials; a fact which is accounted for by its universal distribution, by the ease with which it is worked by simple appliances and comparatively unskilled labor, and by its strength and resistance to wear, to decay, and to the action of mineral waters. But the exhaustion of the supply of cheap timber, combined with the increasing production and decreasing cost of steel, and the appliances for working it, is bringing the latter more and more into competition, especially when the duty is heavy and the wear and tear great. So wooden rails and trucks have long disappeared from metal mining, and now steel and reinforced concrete are coming forward as mine supports. It is not surprising, therefore, that this tendency should extend from the rails and trucks to the chute door, chute lip, and finally to the chute itself. The essential requisites of an ore-pass are, that it must have a life at least equal to that of the stope it serves, a minimum tendency to hang up, a fitness for stoping conditions, and the universal desiderata of small first cost and maintenance.