For a long time they sat comparing their specimens.

Then Frank said, "Come along, it is time to be moving." As he rose to his feet he uttered an exclamation of dismay.

Although the tide was still at some little distance from the spot where they were sitting, it had already reached the cliffs extending out at either end of the bay.

A brisk wind was blowing on shore, and the waves were already splashing against the foot of the rocks.
The whole party leaped to their feet, and seizing their cans ran off at the top of their speed to the end of the bay.
"I will see how deep the water is," Frank exclaimed; "we may yet be able to wade round." The water soon reached Frank's waist.

He waded on until it was up to his shoulders, and he had to leap as each wave approached him.