Breed to Come by Andre Norton

able to discover what particular device of the Demons governed this. But theirworkings had been discovered by Gammage on hisfirst penetration of the lairs when he had fallen intoone. And they were now accepted by his clan as matter-of-factly as the cave people would accept atrail.
    So borne aloft, they went past three more levels,emerging in a place which startled Furtig, though with all he had seen in the past few days his ability tobe surprised should by now have been dulled. They appeared now to be standing on a ledge with one sideopen to the sky. There was such a sensation of height as to make Furtig crowd back against the stone wall,avoiding that open space.
    "There is a wall there, though it cannot be seen."Foskatt must have sensed his unease. "See here, brother." He walked calmly to the far edge, raised onehand, and rapped against an unseen surface.
    As Furtig observed more closely, he sighted hereand there smears on that transparent covering.
    Morethan a little abashed at his display of timidity, hemade himself join Foskatt and look out, fighting the strong feeling that he was standing on the edge of adrop.
    They were far above the ground level here. A strongmorning sun, which awoke points of glitter from thesides of many of the upward-shooting towers, beamedwarmly at them. Furtig stared in wonder.

    From theground level he had marveled at the height of thelairs. But from this vantage point he could see evenmore. He had had little idea of the extent of thebuildings before. They seemed to go on and on forever. Even in the far distance there was a hint of more.Had the Demons covered most of this part of theworld with their buildings?
    "Come—later you can climb higher if you wish, seemore. But now is the time to tell Gammage this newthing."
    Foskatt set off at a bold stride. In spite of hisknowledge of the invisible wall, Furtig kept a path closer to the building. They rounded a curve. Fromthis angle he could see a green shading which could only be trees at a distance. It was as if in that direction the lairs narrowed and one could sight open country beyond.
    The corridor ended in a bridge connecting two ofthe towers. Foskatt trotted out on this as one who hasmade the journey-many times. Furtig, in spite of hisdiscomfort, paced close behind, keeping his attentionfocused strictly on the path ahead, glancing neitherright nor left.
    He had always thought that heights did not botherhim—nor had they in the cave world. But this wasnot that natural world, and now, his body tense, hehurried until he was almost treading on his companion's heels in his eagerness to get to the solid securityof the building ahead.
    This time their way was not invisibly walled; instead they were in the lair chambers. Here the wallswere lighted with a brilliance that ran in swirls andloops, patterns that Furtig found he did not care to examine too closely.
    Also, here the floor was soft under his feet, beingcovered with a material, which yielded to pressurewhen he stepped. Without being asked, Foskatt offered explanations as they went.
    "This is the manner of all those rooms where theDemons once lived. They have many unusual things—springs of hot and cold water which flow at thetouch. Sounds—listen, now!"
    But he need not have given that order. Furtig wasalready listening to a sound, or a series of sounds,such as he had never heard before. They certainlycame from no living creature, but apparently from theair about them. Low sounds, lulling in a way. At themoment he could not have said whether he liked whathe heard or not; he only listened and wondered.
    "What makes it?" he asked at last.
    "We do not know. It does not come regularly.Sometimes we walk into a room and sounds begin, stopping when we leave. Sometimes they start withthe coming of dark, just as certain lights come onthen.
    There is so much we do not know! It would—will—take the lifetimes of five times five of such long living Ancestors as Gammage to learn only a few ofthe