Janus walked a few steps, frowning. Then he said, "I remember reading that there is something darned near a perfect circle in nature." He paused a moment. "Potholes." And he looked at me, as mineralogist, to corroborate.
"What kind of potholes?" I asked cautiously. "Do you mean where part of a limestone deposit has dissol—"
"No. I once read that when a glacier passes over a hard rock that's lying on some softer rock, it grinds the hard rock down into the softer, and both of them sort of wear down to fit together, and it all ends up with a round hole in the soft rock."
"Probably neither stone," I told Janus, "would be homogenous. The softer parts would abrade faster in the soft stone. The end result wouldn't be a perfect circle."
Janus's face fell.
"Now," I said, "would anyone care to define this term 'perfect circle' we're throwing around so blithely? Because such holes as Janus describes are often pretty damned round."
Randolph said, "Well...."
"It is settled, then," Gonzales said, a little sarcastically. "Your discussion, gentlemen, has established that the long, horizontal holes we have found were caused by glacial action."
"Oh, no," Janus argued seriously. "I once read that Mars never had any glaciers."
All of us shuddered.