You see, the water works easily through the sand, and you can always tell what the level of the river is, if its banks are sandy, by digging down to where the sand is wet." "Yes," said Tom, "but the river isn't within a hundred feet of us yet." "You are mistaken.

It is within six inches of us," said Sam.
"How's that ?" "Well, this bank is almost exactly level, and when the river gets above its edge it spreads at once all over it.

Now the sand is wet within six inches of the top, and the river is within six inches of the edge of the bank.

When it rises six or eight inches more, it'll be in here, and I'm afraid it will rise that much before morning.

At any rate we must be ready for it." "What can we do ?" asked Tom in alarm.