Polly gazed astonished at the pool's wonders. "It is like fairy-land," she whispered. "I never saw anything so beautiful. Can we come here every day and will the little pools with these queer creatures always be just this way?"
"We can always come at low tide," Molly told her.
"Then I'll always come down here at this time every day."
"But it will not be low tide always at this time," said Molly.
"Oh, won't it?" returned inland little Polly, quite taken aback. "Why won't it?"
Then her uncle told her how the coming in of the tide changes just as the rising of the moon does, and that one must know the difference in time to be sure. Then he went on to explain something about the small creatures which inhabited the pools, the barnacles which covered the rocks up to a certain point.
"Why don't the barnacles go any higher?" asked Polly. "I should think they would grow and grow just like grass does over bare places in the ground.
"They extend only to high water-mark," her uncle told her, "for you see they are fed by the ocean. If you will watch closely, you can see them open and close as the waves come and go."
"Isn't it wonderful?" said Polly in an awe-struck voice.
"I like it best when the tide is up," remarked Molly, "for I don't think all that dark sea-weed that covers the rocks is very pretty."