“Carl!” Breton sank onto a chair, and groped for his cigarettes. “Did you call me earlier? Within the last half hour?”

“No — I’ve been too busy.”

“You’re sure?”

“What is this, John? I told you I’ve been too busy — we’re in serious trouble over the Silverstream survey.”

“It doesn’t check out?”

“That’s right. I made a series of eight random readings in our designated area this morning, and checked with a different gravimeter after lunch. As far as I can tell at this point the initial survey we made last month is completely haywire. The new readings are roughly twenty milligals down on what they should be.”

“Twenty! But that would suggest a much lighter rock formation than we thought. It could mean something like — “

“Salt,” Tougher cut in. “Could you interest the client in a salt mine in place of a cement works?”

Breton put a cigarette into his mouth and lit it, wondering why the world had chosen this particular evening to begin drifting out of focus. “Listen, Carl. We can make two interpretations of these discrepancies. The first is the one you’ve already mentioned — that the limestone we know to lie under that site has changed overnight into salt — and, with your support, I’m ruling that one out right now. The other is that somehow both our gravimeters are out of adjustment — right?”

“I guess so,” Tougher said wearily.

“So we rent a couple of new instruments tomorrow and go over the ground again.”

“I thought you’d say that. Do you know how many miles I covered today, John? I feel like I’ve walked clear across the state of Montana.”

“I’ll go with you next time,” Breton replied. “I need the exercise. See you in the morning, Carl.”

“Yeah, see you. Oh, John — you left out the third possible explanation.”