"Be on your guard," Knox alerted them. "You're dropping alongside the walls of a canyon."
"I have it," returned Plunkett. "The cliffs plunge into a wide valley." He reached for a switch and dropped one of the ballast weights to slow the descent. Thirty meters from the bottom he dropped one more, giving the submersible almost perfect neutral buoyancy. Next he engaged the three thrusters mounted on the outer ends of the lower spheres.
The bottom slowly materialized through the jade gloom into a broken uneven slope. Strange black rock that was folded and twisted into grotesque shapes spread as far as they could see.
"We've come down beside a lava flow," said Plunkett. "The edge is about a kilometer ahead. After that it's another three hundred-meter drop to the valley floor."
"I copy," replied Knox.
"What are all those wormy rocks?" asked Stacy.
"Pillow lava," answered Salazar. "Made when fiery lava strikes the cold sea. The outer shell cools, forming a tube through which the molten lava keeps flowing."
Plunkett kicked in the altitude-positioning system that automatically kept the submersible four meters above the bottom slope. As they glided across the scarred features of the plateau, they spotted the trails of deep crawlers in scattered pools of silt, perhaps from brittle stars, shrimp, or deep-dwelling sea cucumbers that lurked in the darkness beyond the lights.
"Get ready," said Plunkett. "We're about to head down."
A few seconds after his warning, the bottom dropped away into blackness again and the sub nosed over and fell deeper, maintaining its distance of four meters from the steep drop of the canyon walls.
"I have you at five-three-six-zero meters," echoed Knox's voice over the underwater phone.
"Righto, I read the same," replied Plunkett.
"When you reach the valley floor," said Knox, "you'll be on the plain of the fracture zone."
"Stands to reason," Plunkett muttered, his attention focused on his control panel, computer screen, and a video monitor now showing the terrain below Old Gert's landing skids. "There's no bloody place left to go."
Twelve minutes passed, and then a flat bottom loomed up ahead and the sub leveled out again.
Underwater particles swirled by the sphere, driven by a light current like flakes of snow. Ripples of sand stretched in front of the circular lit pattern from the lights. The sand was not empty. Thousands of black objects, roundly shaped like old cannonballs, littered the seabed in a thick layer.
"Manganese nodules," explained Salazar as though tutoring. "No one knows exactly how they formed, although it's suspected sharks' teeth or whale ear bones may form the nucleus."
"They worth anything?" asked Stacy, activating her camera systems.
"Besides the manganese, they're valued for smaller quantities of cobalt, copper, nickel, and zinc. I'd guess this concentration could run for hundreds of miles across the fracture zone and be worth as high as eight million dollars a square kilometer."
"Providing you could scoop it up from the surface, five and a half kilometers away," Plunkett added.
Salazar instructed Plunkett on what direction to explore as Old Gert soared silently over the nodule-carpeted sand. Then something gleamed off to their port side. Plunkett banked slightly toward the object.
"What do you see?" asked Salazar, looking up from his instruments.
Stacy peered downward. "A ball!" she exclaimed. "A huge metal ball with strange-looking cleats. I'd guess it to measure three meters in diameter."
Plunkett dismissed it. "Must have fallen off a ship."
"Not too long ago, judging from the lack of corrosion," commented Salazar.
Suddenly they sighted a wide strip of clear sand that was totally devoid of nodules. It was as though a giant vacuum cleaner had made a swath through the middle of the field.
"A straight edge!" exclaimed Salazar. "There's no such thing as prolonged straight edges on the seafloor."
Stacy stared in astonishment. "Too perfect, too precise to be anything but manmade."
Plunkett shook his head. "Impossible, not at this depth. No engineering company in the world has the capability to mine the abyss."
"And no geological disturbance I ever heard of could form a clean road across the seabed," stated Salazar firmly.