As he spoke there came a low, growling sound that seemed to proceed
from some distance, but nevertheless filled the air. It rumbled and
rolled above them like--

"Thunder!" exclaimed both boys in the same breath.

"We've got to find shelter of some kind, quick," exclaimed Billy;
"these tropical storms are unlike our little disturbances, and if we
get caught among these trees in one, of them we stand a good chance
of being killed. It looks like we've jumped out of the frying-pan
into the fire."

Without the least idea in which direction they were proceeding, the
two chums struggled bravely on, Billy encouraging the flagging
Lathrop from time to time with a joke, though these latter were, as
Billy admitted to himself:

"Pretty dismal!"

At length, just as dawn was beginning to break, they found
themselves facing a steepish cliff of rough rocks.

"Well, here's where we turn back," remarked Billy, bitterly
discouraged nevertheless.

If they were lost in this equatorial forest, what chance did they
stand of ever seeing their home and friends again?

As for Lathrop he sat down on a rock overgrown with a kind of