"That's right," Cub agreed. "We mustn't forget our mathematics."

"It seems to me that we ought to be able to pick this place on the
chart," Bud suggested.

"Yes, especially if we keep in mind the location of some other landmarks,
or watermarks, that we passed in the last half or three-quarters of an
hour in getting here," said Hal.

Cub produced the chart, and the study of locations and island
arrangements began. As indicated by expectations in the course of their
discussion, they were able to locate a few of the larger islands and with
these as bases for further reckoning, they at last picked out what seemed
to be the point of intersection of the three pencil lines on the chart.
This necessitated a little more cruising about, but within an hour after
their first stop they completed their reckoning.

"There's the island that seems to come nearest to the intersection,"
said Mr. Perry, pointing toward an abrupt elevation, a hundred yards
long and half as wide and covered with bushes and a few small trees;
"but it doesn't seem to answer the description very well. No other
islands near it."

"I don't see how anybody could be marooned on that place with boats
passing back and forth near it every hour of the day," Hal commented
skeptically.

"Neither do I," Bud agreed.

"Well, let's do our work thoroughly anyway," Mr. Perry suggested.