"Forget it," said the exec. "Everybody makes mistakes, even B. S." He leaned back and looked seriously at the biologist. "I have a job I need done. Just now I'm short of men. If you have no objections...."

[Ill.u.s.tration]

The exec was always short of men, would be until the planet was overcrowded, and he would try to find someone to do the work his own men should have done. Dano Marin was not directly responsible to Hafner; he was on loan to the expedition from Biological Controls.

Still, it was a good idea to cooperate with the executive. He sighed.

"It's not as bad as you think," said Hafner, interpreting the sound correctly. He smiled. "We've got the digger together. I want you to run it."

Since it tied right in with his investigations, Dano Marin looked relieved and showed it.

"Except for food, we have to import most of our supplies," Hafner explained. "It's a long haul, and we've got to make use of everything on the planet we can. We need oil. There are going to be a lot of wheels turning, and every one of them will have to have oil. In time we'll set up a synthetic plant, but if we can locate a productive field now, it's to our advantage."

"You're a.s.suming the geology of Glade is similar to Earth?"

Hafner waggled his hand. "Why not? It's a nicer twin of Earth."

Why not? Because you couldn't always tell from the surface, thought Marin. It seemed like Earth, but was it? Here was a good chance to find out the history of Glade.

Hafner stood up. "Any time you're ready, a technician will check you out on the digger. Let me know before you go."

Actually, the digger wasn't a digger. It didn't move or otherwise displace a gram of dirt or rock. It was a means of looking down below the surface, to any practical depth. A large crawler, it was big enough for a man to live in without discomfort for a week.

It carried an outsize ultrasonic generator and a device for directing the beam into the planet. That was the sending apparatus. The receiving end began with a large sonic lens which picked up sound beams reflected from any desired depth, converted it into electrical energy and thence into an image which was flashed onto a screen.

At the depth of ten miles, the image was fuzzy, though good enough to distinguish the main features of the strata. At three miles, it was better. It could pick up the sound reflection of a buried coin and convert it into a picture on which the date could be seen.

It was to a geologist as a microscope is to a biologist. Being a biologist, Dano Marin could appreciate the a.n.a.logy.

He started at the tip of the peninsula and zigzagged across, heading toward the isthmus. Methodically, he covered the territory, sleeping at night in the digger. On the morning of the third day, he discovered oil traces, and by that afternoon he had located the main field.

He should probably have turned back at once, but now that he had found oil, he investigated more deliberately. Starting at the top, he let the image range downward below the top strata.

It was the reverse of what it should have been. In the top few feet, there were plentiful fossil remains, mostly of the four species of mammals. The squirrel-like creature and the far larger grazing animal were the forest dwellers. Of the plains animals, there were only two, in size fitting neatly between the extremes of the forest dwellers.

After the first few feet, which corresponded to approximately twenty thousand years, he found virtually no fossils. Not until he reached a depth which he could correlate to the Late Carboniferous age on Earth did fossils reappear. Then they were of animals appropriate to the epoch. At that depth and below, the history of Glade was quite similar to Earth's.

Puzzled, he checked again in a dozen widely scattered localities. The results were always the same--fossil history for the first twenty thousand years, then none for roughly a hundred million. Beyond that, it was easy to trace the thread of biological development.

In that period of approximately one hundred million years, something unique had happened to Glade. What was it?

On the fifth day his investigations were interrupted by the sound of the keyed-on radio.

"Marin."

"Yes?" He flipped on the sending switch.

"How soon can you get back?"

He looked at the photo-map. "Three hours. Two if I hurry."

"Make it two. Never mind the oil."

"I've found oil. But what's the matter?"

"You can see it better than I can describe it. We'll discuss it when you get back."

Reluctantly, Marin retracted the instruments into the digger. He turned it around and, with not too much regard for the terrain, let it roar. The treads tossed dirt high in the air. Animals fled squealing from in front of him. If the grove was small enough, he went around it, otherwise he went through and left matchsticks behind.

He skidded the crawler ponderously to halt near the edge of the settlement. The center of activity was the warehouse. Pickups wheeled in and out, transferring supplies to a cleared area outside. He found Hafner in a corner of the warehouse, talking to the engineer.

Hafner turned around when he came up. "Your mice have grown, Marin."

Marin looked down. The robot cat lay on the floor. He knelt and examined it. The steel skeleton hadn't broken; it had been bent, badly. The tough plastic skin had been torn off and, inside, the delicate mechanism had been chewed into an unrecognizable ma.s.s.

Around the cat were rats, twenty or thirty of them, huge by any standards. The cat had fought; the dead animals were headless or disemboweled, unbelievably battered. But the robot had been outnumbered.

Biological Survey had said there weren't any rats on Glade. They had also said that about mice. What was the key to their error?

[Ill.u.s.tration]

The biologist stood up. "What are you going to do about it?"

"Build another warehouse, two-foot-thick fused dirt floors, monolithic construction. Transfer all perishables to it."

Marin nodded. That would do it. It would take time, of course, and power, all they could draw out of the recently set up atomic generator. All other construction would have to be suspended. No wonder Hafner was disturbed.

"Why not build more cats?" Marin suggested.

The executive smiled nastily. "You weren't here when we opened the doors. The warehouse was swarming with rats. How many robot cats would we need--five, fifteen? I don't know. Anyway the engineer tells me we have enough parts to build three more cats. The one lying there can't be salvaged."

It didn't take an engineer to see that, thought Marin.

Hafner continued, "If we need more, we'll have to rob the computer in the s.p.a.ceship. I refuse to permit that."

Obviously he would. The s.p.a.ceship was the only link with Earth until the next expedition brought more colonists. No exec in his right mind would permit the ship to be crippled.

But why had Hafner called him back? Merely to keep him informed of the situation?

Hafner seemed to guess his thoughts. "At night we'll floodlight the supplies we remove from the warehouse. We'll post a guard armed with decharged rifles until we can move the food into the new warehouse.

That'll take about ten days. Meanwhile, our fast crops are ripening.

It's my guess the rats will turn to them for food. In order to protect our future food supply, you'll have to activate your animals."

The biologist started. "But it's against regulations to loose any animal on a planet until a complete investigation of the possible ill effects is made."