chunk: Upon reaching Xanthus, a desert region outside the Mare Cimmerium, Jarvis and Tweel find a line of small pyramids tens of thousands of years old made of silica bricks, each open at the top. As they follow the line, the pyramids slowly become larger and newer. By the time the pyramids are ten feet high, the travelers reach the end of the line and find a pyramid that is not open at the top. As they watch, a creature with gray scales, one arm, a mouth and a pointed tail pushes its way out of the top of the pyramid, pulls itself several yards along the ground, then plants itself in the ground by the tail. It starts exhaling bricks from its mouth at ten-minute intervals and using them to build another pyramid around itself. Jarvis realizes that the creature is silicon-based rather than carbon-based; neither animal, vegetable nor mineral, but a little of each. The strange combination of a creature produces the solid substance silica and builds itself in with the by-product, then sleeps for