Straight after the whale it went. One moment the latter was visible. Then a great wall of blackness loomed up and the whale vanished.
Not recognizing the nature of this trick, and fearing a dangerous obstacle, Frank pressed the lever forward and brought the boat to a stop.
“Great Scott!” cried Stanhope, excitedly, “it is a big submarine cave, Frank.”
“A cave!” gasped the young inventor.
“Certainly. A cave under the sea. The whale has gone into it.”
This was certainly the truth.
Frank was greatly surprised. He gazed into the mouth of the cavern in amazement.
It extended far into the bowels, of the earth.
Frank brought the searchlight to bear upon the inner regions of the cave.
A wonderful sight was revealed.