This was now much diversified by hills and even mountains.
There were innumerable caves, many of which were of enormous depth.
In fact the Dart once sailed into one of these nearly half a mile before it was discovered by the voyagers that they were in a cave.
Then, of course, it was in order to turn about and sail out, but before this was done a thrilling experience was had.
Prof. Von Bulow was greatly interested in this wonder of the ocean depths—this submarine cave of the great Atlantic Valley.
“There is nothing like it on top of the earth,” he declared. “I would like very much to examine its structure, which has the appearance of being quartz.”
“Quartz!” exclaimed Captain Bell.
“Yes.”
“Not of the gold-bearing species?”
“It is not impossible.”