All morning they had been tramping through woodlands. At noon they came to the edge of one wood. A clearing stretched ahead of them.
On the edge of this clearing they sat down to their luncheon. While the two chums were eating they heard the strangest and most peculiar noise either of them had ever listened to in their lives. It was the tramping and rushing of many feet, like a charge of cavalry. Once or twice before, since they had taken up their abode on the island, the girls had caught a faint, far-off echo of just such a sound. To-day it sounded much nearer.
"What was that?" demanded Phil quickly, raising her hand.
"It sounds like a cavalry charge," returned Madge, trying to smile, though feeling vaguely alarmed.
The noise swept nearer, like the rush of the wind. Then it stopped as abruptly as it had begun.
Neither girl offered to stir from under the tree where they had halted in order to go on with their pilgrimage. The mystery of the noise that they had just heard made their adventure seem far more perilous. What on earth was it? What did it mean?
The atmosphere was clear. The travelers guessed they must have come to about the center of the island. It was a broad, open plateau, covered with grasses and wild flowers. Neither of the girls thought of how curious it was to find the grass cropped as close to its roots as though it had been cut down by a mowing machine.
Phil was walking slowly ahead. There was an opening through a double avenue of trees, and Phil wanted to find out whether they could get through the woods by this cut. For the moment Madge's back was turned to Phil. She was reaching up for a particularly splendid bunch of Virginia creeper that clung to a branch over her head.
Like a roll of thunder from a clear sky, or the rumble of heavy artillery, came the noise that they had heard before. It was indeed the rushing of many feet and it was coming nearer.
Phil ran toward a low-branched tree. "Climb the tree, Madge!" she cried.