It sometimes happens that minerals occur in the form of conical masses, resembling icicles, which in many instances have a hole running through their center. Carbonate of lime offers t!io most numerous examples of this kind of formation, which is commonly occasioned by the dropping of water from the roof of a cavern. In this case, the water surcharged with carbonic acid holds the carbonate of lime in solution, and when that escapes, the mineral is deposited in the solid form. The cones thus depending from the roof have received the name of stalactites, and are, in most instances, placed immediately over similar formations on the floor, called stalagmites, by the union of which with the stalactites above, complete pillars, from the floor to the roof, are occasionally produced. Chalcedony and brown iron ore also occur in the form of stalactites.