Jane said, “You don’t talk to kids much, do you?”

“I know about the craters on the Moon,” Jack said. “Like Tycho.”

“Well, that’s good.”

“Are the craters volcanoes?”

“No. The craters are impact scars. But we used to think they were volcanic. You know, they took the Apollo astronauts crawling over Hawaii for their training, the big volcanic calderas there. All those lava surfaces. They thought the Moon would be like that. Wrong… They should have stayed on the beaches; that turned out to be a closer match. Anyway I hate Hawaii.”

“Why?”

“I was once studying active lava flows there, and I broke through a solid crust and sank into molten lava up to my knees. Not pleasant. But I recovered.”

“Wow,” said the kid, round-eyed. “Is lava dangerous?”

“No. Lava is friendly. Unless you’re unlucky, or careless, like I was. You can walk around on lava. It smells odd, like scorching paper. And it moves slowly; you can get away from it. Pyroclastic flows are what you have to look out for if you’re ever close to a volcano.”

“Pyro—”

“Ash.”

Ted helped himself to more chili. “So why do all geologists look like they’ve been living in a hole in the ground?” Jane laughed.

Mike said, “They probably have, dad.”

Henry said, “It’s true. There are other types of people who study the Earth. Like photogeologists, for instance, who work from photographs, and petrologists, who treat their rocks like lab specimens, and geochemists and geophysicists. But old-time geologists will look down their noses at any of that and say, ‘Needs field checking’. By which they mean, if you can’t walk on it and rub your hands in it and get yourself good and dirty in it, it ain’t geology.”

“Hey,” Mike said. “I have a joke about that. Maybe you heard it. What’s 2 plus 2? The geologist says, ‘Well, around 4.’ The geochemist says, ‘4 plus or minus 2.’ The geophysicist says, ‘What number do you want?’”

Henry laughed, though he’d heard it before. The others just looked baffled. “So,” said the father. “You divorced, separated or what?”

After the meal, Mike’s father said he would wash up, and Mike and Jack went out to the garden to play some more football.

Jane and Henry sat in the living room, regarding each other warily.

Jane said unexpectedly, “You want to go for a walk?” She stood briskly. “We’ll climb the Seat. Shouldn’t take more than an hour. Unless you think that’s too far.”

Henry stood. “I’ll be fine.”

She handed Henry a heavy radiation-screen poncho, and marched him out the door and down the path.

They tramped for a brisk half-mile on the road, going north-east, skirting the base of the Seat. Then they turned off and began to climb a path over the Seat itself. Soon, Henry was walking over spongy grass, with hard basalt beneath, tough through the soles of his training shoes.