A stone sat on the ground, vibrating with the loudness of the sounds it blared out.
"What manner of music is this?" Magnus demanded.
"Why," said the rock, " 'tis but entertainment."
"It doth glisten," Cordelia murmured.
Geoffrey frowned. "Is't wet?" He reached out to touch it.
"Geoffrey, no!" Fess cried, and the boy, from long experience with Fess, halted. "An thou sayest it, I'll stay. I've ne'e'er known thy judgment to be false. Yet what need for caution dost thou see?"
"A rock that glistens when no water is near, is suspect," Fess explained. "I mistrust the nature of its moisture."
"Oh, 'tis naught of evil!" Cordelia scoffed. "Art thou, rock?"
"Nay," the rock answered, and the children started, for the rock now spoke by modulating the strains of its music. " 'Tis but entertainment."
Gregory cocked his head, studying the sound. "This is yet a different sort of sound that it doth give."
"Perhaps a minor variation…" Fess allowed.
"Nay, 'tis truly new!" Cordelia tried to match both beat and bray with her feet, failed, and had to writhe her body to fit both. She gyrated, crying, " 'Tis harsh, but 'tis filled with verve!"
Magnus stared at her, shaken by her sinuous movements.
Geoffrey shook his head, dissatisfied. " 'Tis not a proper sound. Its beat is too uneven."
"'Tis oddly structured, in truth." But Gregory was beginning to look interested. "Nay, I sense some interlocking between two sorts of counts…"
"It is employing two different time signatures in the same piece," Fess said briskly. "Surely that is elementary enough."
"Why, so it is!" Gregory cried. "How ingenious!"
"Largely instinctive, I fear," Fess demurred.
"And the tune! Note how the strains approach one another, till the two notes are almost one, yet not quite! Anon they strengthen one another; anon they war!"
"Yes; the product of their phases is termed a beat frequency, Gregory. Surely you cannot acclaim a lack of skill as ingenuity…"
"Can we not, if they do it a-purpose?" Cordelia countered.
"I mislike it." Geoffrey started to reach for the stone again. "Let us hurl it far from us."
"No, Geoffrey! I beg you, before you touch it, to perform a simple test!"
Reluctantly, the boy straightened. "What test is this?"
"An acid test. Reach in my saddlebag, and take out the environmental kit."
Frowning, Geoffrey reached up, rummaged, and came up with a metal box.
"Open it," Fess said, "and take out the tube filled with blue slips."
"The litmus paper?" Gregory was surprised. "What dost thou think it to be, Fess?"
Geoffrey laid the box on the ground, lifted the lid, and took out a clear plastic tube. "Shall I take a strip of it?"
"Do, and touch it to the rock."
Geoffrey pulled out the litmus and reached out to touch; the stone giggled.
The paper turned bright pink.
Then it began to smoke, darkening; a hole appeared and spread. Geoffrey dropped it with an oath, just before the whole strip of paper disappeared, leaving only a fume behind.
"What was it?" Cordelia whispered, shocked.
"The rock is coated with acid," Fess explained. "I suspect that it exudes the fluid. Put the kit away, Geoffrey."
"Aye, Fess." Geoffrey bent to stopper the tube and put it back in the box. "And I thank thee. Would my skin have burned had I touched that rock?"
"I do not doubt it… Yes, back in my saddlebag, that is correct."
"Yet what are we to do with this thing?" Magnus looked at the stone. "We cannot leave it here, to eat through any living creature that doth chance to wander by."
Cordelia shuddered.
Fess looked up, nostrils catching the breeze—and feeding it to molecular analyzers. "I detect a familiar aroma… Geoffrey, look beyond those trees."
Geoffrey stepped over. "I see a small pit, perhaps a yard across, filled with some white powder."
"It is alkali; I know it by the aroma. The problem is solved, at least in this instance. Geoffrey, take a fallen stick and bat the stone into the pit."
Geoffrey turned, coming back, stooped, and came up with a four-foot branch. He took his stance by the stone and swung the stick up. As it swooped down, the stone saw, and in alarm, shrilled, "Do not knock the rock!" But Geoffrey had too much momentum, and wasn't about to stop anyway; the end of the stick connected with the stone, and it flew through the air, emitting a keening drone, to land in a puff of powder.
"Well aimed, Geoffrey," Fess approved.
But the boy was staring at his accomplishment. "What doth happen to it?"
The rock was drying out and, as they watched, gained an odd, crinkled texture, with here and there a glint of reflected light. The music changed, too, gaining a new sort of piercing twang.
"Its surface has undergone a chemical change," Fess explained. "It exuded acid—but you sent it into a pit of alkali, which is a base."
"Then I have scored it with a base hit?"
"And bases and acids combine to produce salts!" Gregory said. "But why doth it glisten so, Fess?"
"Presumably this alkali was a compound of one of the heavier elements, children—or perhaps even the acid itself was. In any event, the salt is metallic."
"Aye—there is something of that in the sound." Cordelia cocked her head to the side, listening.
"But how could a soft rock turn into an acid rock?" Gregory wondered.
"An excellent question, Gregory—and one which I am sure we will find answered as we journey farther west." Fess turned his back on the alkali pit. "Come, young friends. I confess I have grown curious as to the manner of the transformation, for it is one I have never seen on Gramarye before."
"Aye!" Cordelia skipped to join him. "That is the wonder of it—that it is so new!"
Her brothers fell in behind her with varying degrees of eagerness, and marched away, following their equine guide.
Behind them, the alkali pit emitted a steady stream of sound, growing harsher and harsher as the rock hardened.
Suddenly, with a sharp report, two rocks sprang out of the pit, sailing away eastward. They flew in long flat arcs, ninety degrees apart, and when they came to earth, their music was louder.
Chapter Twelve
The day was waning as they came to a riverbank. Cordelia sank down. "Let us stay the night here, Fess, I pray thee! For I'm overborne with the toils of this day, and must rest!"
Fess tested the breeze with electronic sensors. "Not here, young friends, for the trees grow too close to the edge of the water. Only a little farther, I pray you."
"Courage, sister." Magnus extended a hand. "Tis only a little way. Lean thou on mine arm."
"Oh, I can bear mine own weight." Cordelia caught his hand and pulled herself upright. " 'Tis only the burden of all the things we've seen that doth weigh on me."
"On me, also," Gregory said.
"Aye," said Geoffrey, "yet thou art wearied by efforts other than ours, brother." He forced himself to stand straight. Together, they turned to follow the black horse, whose outline was beginning to be obscured by the dusk.
Gregory tried to blink away the sleepiness. "How dost thou mean, effort other than thine?"
"Why," said Geoffrey, "I am wearied by marching or battle, but thou art wearied by striving to comprehend anything that confounds thee."
"Everything is comprehensible," Gregory muttered. " Tis only a matter of striving, until it comes clear."
"True," said Fess. "Some problems, however, require generations of striving."
"Well, true," the little boy admitted. "Yet such riddles as those, I can tell apart in a few hours' time. 'Tis the ones for which I've all the knowledge I should need that confound me."