"The water's higher," said Andy, in a low voice. Frank had noticed that, for it now reached to his ankles as he splashed his way back along the passage. But he had said nothing, hoping Andy had not observed it.
"Yes," said the older boy cheerfully, "It's bound to rise until the tide is at flood, and then—why, it will go down again—that's all."
"But suppose it fills this cave?"
"Nonsense! It can't. I'm not going to suppose anything of the sort.
Now come on. Let's see if we can move this rock."
Together they pressed on the stone with all their strength. They might as well have tried to budge the side of a mountain. The rock was firmly wedged in place.
"It's no use," spoke Andy, in a dull, hopeless tone.
"Oh, don't give up so easily," urged his brother. "If we can't do it one way, we may another. See, it has slid down in a sort of groove. Only a little ridge of rock on either side holds it in place. Now if we can break away those upright ridges, which are like the pieces on a window sash up and down which the window slides, we may be able to push the rock out. Let's try. Use your knife and take a rock for a hammer."
Frank placed his torch on a ledge of rock, tying the spring down by a piece of cord so that the light would focus on the big bowlder. Then, with their pocket-knives as chisels, and stones as mallets, they began their futile attempts to cut away the holding ridges of rock.
That it was a futile attempt was soon made evident, for their knives slipped off the flint-like stone, and several times when the blades unexpectedly shut, the lads received severe cuts on their hands.
Suddenly Andy uttered an exclamation: