The pilasters, which are almost universal in kivas of the first type, as has been shown in the description and illustrations of the eight kivas of Spruce-tree House, served as supports for the roof beams. These rafters of pine rested upon and served to support other logs laid one over another, so that finally the roof opening was covered. Across the middle of the walls, at the top, two long parallel logs were placed, in order to add stability to the roof structure. These beams were set far enough apart to allow a hatch midway between their ends, which served the purpose of an entrance and also permitted the escape of smoke from the fire directly below. Over the framework of logs were laid small sticks, filling the interstices, and above these was spread a layer of cedar bark; the whole was then covered with clay, thus bringing the upper surface of the roof to the level of the adjacent plaza. Whether the kiva walls projected above the plaza and roof level is unknown, but possibly they did, and there may have been a slight elevation of the hatchway, as in the Hopi kivas. It is commonly believed that the kiva roof was level with the surrounding plaza and that the entrance was through a hatchway, but no depression or other sign of a ladder or of its resting place on the kiva floor has yet been found in any of the Mesa Verde ruins. The floors of the kivas are commonly of hardened adobe; unlike those of the Hopi kivas they are never paved with stones, but the natural rock often serves for that purpose. It is not rare to find the surface of solid rock that forms the kiva floor cut down a few feet to a lower level. Although generally smooth, when the floor is the natural rock there are sometimes found in it small, cup-like, artificial depressions similar to those in the horizontal surfaces of the cliff or in slabs of detached rock. The fire-pit, which is found in all kivas of the first type,[47] is a circular depression situated slightly to one side of the middle of the room. While generally lined with adobe, slabs of stone sometimes form its border, and it is also to be noted that one or two of these small stones sometimes project above the floor level. The fire-hole is sometimes deep, and is generally filled with wood ashes, indicating long use. [Footnote 47: The fire in these rooms was more for light than for heat, for when roofed a large fire would have produced so much smoke and heat that the occupants would be driven out. The character of the ashes indicates that logs were not used as firewood, but that the prescribed kiva fuel was, as at Walpi, small twigs or brush. No evidence of lamps has been found in cliff-dwellings, the lamp-shaped pottery objects having been used for purposes other than illumination.]