a microscope to see them."

"I don't quite see why," said Ross. "I know bigger things are heavier,
but why should a big bit of earth sink more quickly than a small bit,
when they're both made of just exactly the same stuff?"

The Weather Man looked at him.

"Some of these days," he said, "remind me to talk to you about sunlight
and dust, and I'll tell you a heap of things you don't know. Right now,
get this idea in your head. The larger a piece of matter is, the smaller
is the surface in proportion to the bulk. A feather of swan's down will
float in a high wind, but if you roll that feather into a ball, it will
fall. Why? You haven't made it any heavier. You've only reduced the
amount of surface which was borne up by the air. It's the same way with
mud, the bigger pieces sink first because they have less surface in
proportion to their weight."

"Yes," answered Ross, "I can see that now."

"Very good, then," the Forecaster continued, "when the Mississippi
overflowed its banks and the water got out of the current of the main
stream, so that it flowed more gently, the sediment began to fall, the
larger pieces first and those that were finer until it was only at the
most distant point from the river that the finest mud settled. This has
gone on, year after year, for thousands of years.

"Therefore, you see, the lands nearest the river are higher than those
farther away. In two big basins, the St. Francis and the Yazoo basins,
the slope and the drainage is away from the river, instead of towards
it."

"In that case, then," said Anton thoughtfully, "the Mississippi runs in
a groove on the top of a hill."

"That's it exactly," the Forecaster said, "and some of the most fertile
fields lie in the lowlands made of the fine mud at the bottom of this
hill. It's just like that hollow where your house was, Anton. The flood
hasn't done much damage south of here because all the waters poured down
into that fine plantation land where your place was located."

"What I don't see," said Ross, "is why the Government doesn't build a
really high levee all the way along the river. I don't mean just a few
feet higher, but a regular wall 'way higher than the river ever goes. I
mean a regular stone wall, twice as high as any levee that we've got
now. I should think that would make the river behave."

"It would and it wouldn't," replied the Weather Man. "What are you going
to build that wall on? On the ground?"

"I suppose so," said R