“Be not so sure,” said Frank.
“Why?”
“The continent may have been only an island, and this is possibly the only city upon it.”
All reflected that this might be true.
Thus the discussion progressed for some time, no definite conclusion being reached.
At length it was decided to leave the sunken city and proceed on the way to the end of the valley.
Accordingly Frank went into the pilot-house and started the Dart.
The submarine boat floated away over the housetops and soon left the sunken city behind.
As the Dart went on now many traces of a once powerful civilization were to be seen.
There were many buildings which might have been country houses or farms once.