There is nothing impossible in the theory that they found shelter at last up here.

As long as history runs this has been a well-nigh unknown land.

Penetrating some mountain-guarded, easily defended valley they might have decided to settle down for a time, have rebuilt a city, raised a government; laying low, in a sentence, waiting for the storm to blow over.
"Why did they stay?
Well, they might have found the new life more pleasant than the old.

And they might have been locked in their valley by some accident--landslides, rockfalls sealing up the entrance.

There are a dozen reasonable possibilities." "But those who hunted you weren't locked in," objected Drake.
"No," Ventnor grinned ruefully.