Oil!

Bunny and Rachel had dinner, and then strolled on the waterfront; it was one of those warm nights that come now and then in Southern California; there was a moon on the sea, and a long pier with gleaming lights, and the sound of an orchestra drawing the lovers. At the entrance to the pier was a big bare hall, owned by the city, where very proper dancing was chaperoned by a religious city government. Bunny and his bride danced -- oh, surely it was all right to dance a little bit, in this well chaperoned place on what ought to have been their honeymoon!

But in between the dances, while the orchestra was still, something shook the hall, a dull, sombre blow, like distant thunder, making the windows rattle, and jarring your feet. "What's that? " exclaimed Rachel. "An earthquake?"