This petrel digs itself a little burrow and lays one egg. The burrow might hold both birds at once, but one seldom finds two birds in the burrow together. While one is brooding, the other is off on its wonderful wings--away off in the wake of your ocean steamer, perhaps, miles and miles from shore. But when darkness falls it remembers its nest and speeds home to the rock, taking its place down in the little black burrow, while the mate comes forth and spreads its wings out over the heaving water, not to return, it may be, until the night and the day have passed and twilight falls again. We landed on a ledge of Shag Rock, driving off a big bull sea-lion who claimed this particular slab of rock as his own. We backed up close to the shelf in a yawl boat, and as the waves rose and fell, watched our chance to leap from the stern of the little boat to the rock. Thus we landed our cameras, food and water, and other things, then we dragged the boat up, so that, a storm arising or anything happening to the small steamer that had brought us, we might still get away to the shore. It was about the middle of the forenoon. All the morning, as we had steamed along, a thick fog had threatened us; but now the sun broke out, making it possible to use our cameras, and after a hasty lunch we started for the top of the rock--a climb that looked impossible, and that was pretty nearly as impossible as it looked. It had been a slow, perilous climb; but, once on the summit, where we could move somewhat freely and use the cameras, we hurried from colony to colony to take advantage of the uncertain sunlight, which, indeed, utterly failed us after only an hour’s work. But, as I had no camera, I made the best of it, giving all my time to studying the ways of the birds. Besides, I had come to stay on the peak all night; I could do my work well enough in the dark. But I could not do it in the wind and rain. The sun went into the clouds about four o’clock, but so absorbed was I in watching, and so thick was the air with wings, so clangorous with harsh tongues, that I had not seen the fog moving in, or noticed that the gray wind of the morning had begun to growl about the crags. Looking off to seaward, I now saw that a heavy bank of mist had blurred the sky-line and settled down upon the sea. The wind had freshened; a fine, cold drizzle was beginning to fall, and soon came slanting across the peak. The prospect was grim and forbidding. Then the rain began. The night was going to be dark and stormy, too wet and wild for watching, here where I must hang on with my hands or else slip and go over--down--down to the waves below. We started to descend at once, while there was still light enough to see by, and before the rocks were made any slipperier by the rain. We did not fear the wind much, for that was from the north, and we must descend by the south face, up which we had come.