"After emerging from the Ice Stone," he explained, "I had to discard my outer clothing. The sudden climatic change was almost shocking." Then he pointed upward and to the left along a broad ledge that seemed to zigzag down the rough face of a cliff, a hundred yards away. I guess Doc Champ had already caught sight of the Ice Stone. But I hadn't; and now with my first glimpse of it, the thing did look exactly like ice. It was like a huge, square block, set flush with the face of the cliff, and with that ledge forming a pathway up to it. "Queer," I heard Doc Champ muttering. "All the legends pertaining to the Ice Stone mention its black appearance. That stone doesn't look black--it looks transparent." "Its color has recently changed," explained Rog Tanlu. "It isn't a stone, or any material substance. It is a peculiar kind of space--space with the third dimension, thickness in this instance, so twisted and curved as to allow the fourth dimension to emerge from nothingness into a certain hypostatic realness. Light has needed a long time to penetrate through it, and for that reason the cube has only recently assumed an apparent transparency. Now, if you will follow me, I will lead you to my laboratory." He continued on around a shoulder of the cliff, so that we lost sight of the Ice Stone. Gigantic boulders all but blocked the way. However, our strange guide seemed to know where he was going and how to get there. "All these rocks didn't used to be here," he said musingly. "They are evidently glacier débris carried down since--well, since my time. Ah! Here we are." He wormed his way through a narrow crevice. Doc and I followed. We soon entered what at one time in the past must have been the wide mouth of an underground cavern. For a moment we stood there, breathing the cold, moist air and staring into the darkness. Suddenly a light flashed. I saw that Rog Tanlu was using that fountain-pen thing like a flashlight, but now it was sending out a blue-white radiance instead of those thin, death-dealing flashes. "This was my laboratory," he said, holding the light at arm's length above his head. "There were big sliding doors that closed the place up tight and kept out the ice and the cold. I had some rather unique scientific apparatus here, but now it's all mouldering dust." His voice sounded flat, there with the weight of rocks around us, and sad somehow. The floor of the cavern slanted stiffly upward. As we advanced, the air around us kept getting colder and colder. It was like a gale from the poles blowing in our faces. "We'll soon be directly behind the Ice Stone," said Rog Tanlu.