"I suppose it will give them frightful pains," remarked Frances at
last, rising from her cramped position. "Goodness! the tide is
coming!"

"Yes, but it's far out," replied Edith, casting a glance at the
line of water, still distant a full half-mile. "Look, Frances,
here's a tiny pink crab."

For a moment Frances again bent over the aquarium but soon started
to her feet.

"Let's go back, Edith. We're a long way from shore and you know
how very fast the tide comes in."

"Oh, is that crab gone? I thought you would mind where he went,"
said Edith as she reluctantly rose. "I wanted to take him to Win."

The two began to retrace their way, at first over piles of red
rock covered with seaweed, farther on over stretches of sand
surrounding rock islands.

Just as they left the last of the solid rock a big wave came
curling lazily along its side. For a second the water clung to it
like fingers, then withdrew.

"Fran, we must run," said Edith quietly, but her face had grown
pale.

Frances made no reply. Both ran as fast as they could across the
stretch of level hard sand. Before they reached the first rock