From "Manual of Muad'Dib" by the Princess Irulan

If only we had suspensors , Jessica thought. It'd be such a simple matter to jump down there. But perhaps suspensors are another thing to avoid in the open desert. Maybe they attract the worms the way a shield does .
They came to a series of shelves dropping down and, beyond them, saw a fissure with its ledge outlined by moonshadow leading along the vestibule.
Paul led the way down, moving cautiously but hurrying because it was obvious the moonlight could not last much longer. They wound down into a world of deeper and deeper shadows. Hints of rock shape climbed to the stars around them. The fissure narrowed to some ten meters' width at the brink of a dim gray sandslope that slanted downward into darkness.
"Can we go down?" Jessica whispered.
"I think so."
He tested the surface with one foot.
"We can slide down," he said. "I'll go first. Wait until you hear me stop."
"Careful," she said.
He stepped onto the slope and slid and slipped down its soft surface onto an almost level floor of packed sand. The place was deep within the rock walls.
There came the sound of sand sliding behind him. He tried to see up the slope in the darkness, was almost knocked over by the cascade. It trailed away to silence.
"Mother?" he said.
There was no answer.
"Mother?"
He dropped the pack, hurled himself up the slope, scrambling, digging, throwing sand like a wild man. "Mother!" he gasped. "Mother, where are you?"
Another cascade of sand swept down on him, burying him to the hips. He wrenched himself out of it.
She's been caught in the sandslide , he thought. Buried in it. I must be calm and work this out carefully. She won't smother immediately. She'll compose herself in bindu suspension to reduce her oxygen needs. She knows I'll dig for her .
In the Bene Gesserit way she had taught him, Paul stilled the savage beating of his heart, set his mind as a blank slate upon which the past few moments could write themselves. Every partial shift and twist of the slide replayed itself in his memory, moving with an interior stateliness that contrasted with the fractional second of real time required for the total recall.
Presently, Paul moved slantwise up the slope, probing cautiously until he found the wall of the fissure, an outcurve of rock there. He began to dig, moving the sand with care not to dislodge another slide. A piece of fabric came under his hands. He followed it, found an arm. Gently, he traced the arm, exposed her face.
"Do you hear me?" he whispered.
No answer.
He dug faster, freed her shoulders. She was limp beneath his hands, but he detected a slow heartbeat.
Bindu suspension , he told himself.
He cleared the sand away to her waist, draped her arms over his shoulders and pulled downslope, slowly at first, then dragging her as fast as he could, feeling the sand give way above. Faster and faster he pulled her, gasping with the effort, fighting to keep his balance. He was out on the hard-packed floor of the fissure then, swinging her to his shoulder and breaking into a staggering run as the entire sandslope came down with a loud hiss that echoed and was magnified within the rock walls.
He stopped at the end of the fissure where it looked out on the desert's marching dunes some thirty meters below. Gently, he lowered her to the sand, uttered the word to bring her out of the catalepsis.
She awakened slowly, taking deeper and deeper breaths.
"I knew you'd find me," she whispered.
He looked back up the fissure. "It might have been kinder if I hadn't."
"Paul!"
"I lost the pack," he said. "It's buried under a hundred tons of sand . . . at least."
"Everything?"
"The spare water, the stilltent—everything that counts." He touched a pocket. "I still have the paracompass." He fumbled at the waist sash. "Knife and binoculars. We can get a good look around the place where we'll die."
In that instant, the sun lifted above the horizon somewhere to the left beyond the end of the fissure. Colors blinked in the sand out on the open desert. A chorus of birds held forth their songs from hidden places among the rocks.
But Jessica had eyes only for the despair in Paul's face. She edged her voice with scorn, said: "Is this the way you were taught?"
"Don't you understand?" he asked. "Everything we need to survive in this place is under that sand."
"You found me," she said, and now her voice was soft, reasonable.
Paul squatted back on his heels.
Presently, he looked up the fissure at the new slope, studying it, marking the looseness of the sand.
"If we could immobilize a small area of that slope and the upper face of a hole dug into the sand, we might be able to put down a shaft to the pack. Water might do it, but we don't have enough water for . . ." He broke off, then: "Foam."
Jessica held herself to stillness lest she disturb the hyper-functioning of his mind.
Paul looked out at the open dunes, searching with his nostrils as well as his eyes, finding the direction and then centering his attention on a darkened patch of sand below them.
"Spice," he said. "Its essence—highly alkaline. And I have the paracompass. Its power pack is acid-base."
Jessica sat up straight against the rock.
Paul ignored her, leaped to his feet, and was off down the wind-compacted surface that spilled from the end of the fissure to the desert's floor.
She watched the way he walked, breaking his stride—step . . . pause, step-step . . . slide . . . pause . . .
There was no rhythm to it that might tell a marauding worm something not of the desert moved here.
Paul reached the spice patch, shoveled a mound of it into a fold of his robe, returned to the fissure. He spilled the spice onto the sand in front of Jessica, squatted and began dismantling the paracompass, using the point of his knife. The compass face came off. He removed his sash, spread the compass parts on it, lifted out the power pack. The dial mechanism came out next, leaving an empty dished compartment in the instrument.
"You'll need water," Jessica said.
Paul took the catchtube from his neck, sucked up a mouthful, expelled it into the dished compartment.