l
up in the wide places and you'd be as badly off as before."

"Make it all the same width, then," said Ross.

"Build two-thirds of the whole two thousand miles by some underwater
system, constructing the wall under water? If you had ever read of the
difficulty of building one lighthouse foundation, my boy, you wouldn't
talk so glibly about building huge retaining masses of masonry under
water."

"Suppose it were done, that way, Mr. Levin," put in Anton, "would that
settle it all?"

"You mean--suppose there was a high masonry wall, making a canal equal
in width and height from St. Louis to the Gulf, would that turn the
Mississippi into a permanent ship channel? Is that what you mean?"

"Yes."

"No, it wouldn't," the expert replied. "What are you going to do with
all the little streams that flow into the Mississippi? Think for a
minute, boys. You can see that wherever you narrow the banks, the river
channel has got to be made deeper to accommodate the water, hasn't it?"

"Yes," both boys agreed, "it has."

"In other words, suppose that before you put up this huge masonry wall,
the flood crest was fifty feet at Memphis, then, after the wall was
built, the flood crest would be seventy-five or a hundred."

"Suppose it were," said Ross, "the wall would hold it in."

"So you think. There are the tributaries to consider. Take the Yazoo,
for example. It flows into the main river until the Mississippi reaches
the fifty-foot flood level. If you raise the flood level of the
Mississippi to seventy-five feet, the water in the main river will be
twenty-five feet higher than the water which used to run into it at the
fifty-foot level, won't it?"

Ross whistled.

"I see where you're coming to," he said; "I'd never have thought of
that. Go ahead, Mr. Levin."

"With the water in the main stream twenty-five feet higher than in the
tributary, due to your retaining wall, boy, instead of the water in the
Yazoo River flowing into the Mississippi, all the water above the
fifty-foot level in the Mississippi would flow into the Yazoo. The Yazoo
couldn't hold the water, and as the stream backed up, it would overflow
its banks. All the low valleys would be flooded in exactly the same way
that they were before, only, instead of the floods coming directly
through a break in the levee or over the banks of the Mississippi, they
would come over the banks of the Yazoo. That would be true of every
small river that flows into the Mississi