"Did you ever hear why that particular rock was called Wolf Rock?"
"No, sir," answered Eric, "I don't think I ever did. Is it because of the shape of it, or because the sea breaking over it is like the fangs of a wolf or something like that? There generally isn't an awful lot of reason for the names of rocks and reefs."
"There is for this one," said his friend. "It isn't because it looks like a wolf, but because it howls like a wolf."
"You mean the fog-horn does?"
"No, I mean the rock does, or did," was the reply.
"How?"
"You've heard of blow-holes?"
"Yes, sir," said Eric, "there's one at the Farallones Islands. You mean those holes that make a noise when the tide comes in and out?"
"That's the idea. The Wolf Rock was a most famous case of that. It had a large cavern inside and a very small hole through the rock at the ceiling of the cavern. Then there was a cleft or fissure through the rock right down to this little hole. You can see for yourself that when the tide started to come in, it closed the sea entrance to the cavern, imprisoning a lot of air. Then, as the tide rose steadily, the pressure of the water drove the air out of the cavern through this little hole, continually making an intermittent blowing sound. The great cleft in the rock acted like the horn of an immense megaphone. This gave rise to a roar, high-pitched—owing to the smallness of the hole—like a wolf's howl. Night and day, but more especially when the tide was coming in, the howl of the Wolf Rock sounded over the sea to warn mariners of the perilous crag."
"Handy," remarked Eric; "it would save the Lighthouse Service a good bit of money if every rock could be fixed like that."