power of the soil is low, and it is very difficult in certain places to maintain the levees at full height; but the principal reason is more convincing:

"New Orleans is one of the leading seaports of the United States. The design of the public wharves along the entire river front was based upon a levee grade several feet below that which is now known to be necessary, if levees are to continue as the sole means of protection. The rail lines and streets serving these wharves have also been built to the lower grade.

"The wharves are not operated for profit, and it is quite certain that the National Government will never embark on a program of building or rebuilding wharves in any city. Raising of the wharves to conform to a higher levee grade would, therefore, be a slow process, probably requiring twenty years, while the raising and revamping of the levee system from above Cairo to the mouth of Red River will quite naturally be effected as quickly as possible.

"For that long reach of river there is no doubt that levees-higher and better levees—are the answer to the flood problem. And no informed person will question the assertion that the close confinement of flood waters from Cairo to Red River will increase the flood menace along the Mississippi below Red River, unless something is done to prevent it.

"For this reason it is necessary that relief measures be effected on the lower river either before or simultaneously with the raising and perfecting of the levees in the upper reaches."

FLOODS WERE FOUGHT BY DE SOTO'S MEN

After De Soto died and was buried in the Mississippi his party was overtaken by high water. A description of this flood of 1543, as set down by Garcilaso de la Vega, in his "La Florida del Ynca," is useful to us in studying the flood problem of to-day. It tends to show very plainly that the floods are not caused, as has often been stated, largely by deforestation, ditching, draining, and plowing up of the original grass mat in so many States drained by the river.

De Soto's men, after their failure to push westward, again set about building

boats in which to pass down the Mississippi and across the Gulf to Mexico. It was then the flood came. De la Vega says:

"Then God, our Lord, hindered the work with a mighty flood of the great river, which, at that time (about March, 1543), began to come down with an enormous increase of water, which in the beginning overflowed the wide level ground between the river and the cliffs; then little by little it rose to the top of the cliffs. Soon it began to flow over the fields in an immense flood, and as the land was level, without any hills, there was nothing to stop the inundation.

"The flood was 40 days in reaching its greatest height, which was the twentieth of April, and it was a beautiful thing to look upon the sea where there had been fields, for on each side of the river the water extended over 20 leagues of land, and all of this area was navigated by canoes, and nothing was seen but the tops of the tallest trees.'

NATURE MAY NEVER HAVE INTENDED THESE RIVER LANDS TO BE CULTIVATED

Since De Soto came much water has rolled this way. It always will. Some thinkers say Nature never meant these marshes to be diked and thickly peopled. Economists insist we farm too much land now. They say the same energy spent on dikes would have earned more had it been applied to farms on higher ground. Maybe so. When you look back at periodic waste from floods, you feel this might be true.

But such pondering is of the past. Now there is no turning back. To-day rich cities stand behind the levees. Sugar factories flourish and sawmills hum. To these, linked by rail and pavement, vast plantations add their income. Here all wealth multiplies and populations grow, just as levee systems improve.

In our complex national economy this rich region plays a big part. When floods menace it, the whole Nation springs to its defense. Engineers say this defense is difficult; history shows it. Perhaps perfect defense can never be, for levees are against Nature. But man persists, like the ant whose hill is plowed. He pays for thwarting Nature's laws when he feels the prize is worth the price.

C

OMPARATIVELY few individuals are aware of the teeming life that may exist in a single glass of sea water. Sometimes a random dip into what is apparently clear water will reveal to the microscope the existence of a world of plants or animals minute in form, yet seemingly limitless in numbers.

This strange world is peculiar to no particular ocean, but is to be found in every quarter of the globe. And, while the organisms that compose it abound to a greater extent in some regions than in others, no place has yet been discovered. where surface waters are entirely free from them.

Furthermore, these organisms are of a rare and unsuspected beauty-a_beauty so totally dissimilar to that which distinguishes the larger and more familiar residents of our planet that there is really no standard of comparison.

To this population of small floating plants and animals the term Plankton has been applied; but, in the strict modern usage of the word, Plankton is taken to include also nearly all creatures that can swim, regardless of their size or of the depth at which they live, as distinguished from those that are fixed to or actually crawl upon the bottom.

MINUTE SEA LIFE FEEDS GIANT WHALES

So abundant is this minute sea life that a creature as gigantic as the Greenland whale, which often attains a length of 45 or 50 feet, subsists solely upon it. One can appreciate, therefore, the truth of the remark of the late Prince of Monaco, famous oceanographer, to the effect that no shipwrecked sailor adrift in a boat or on a raft need starve if equipped with a simple muslin net.

of

Tiny as these sea forms are, many them secrete shells. As the living organisms die, their shells settle to the floor of the ocean, in some regions comprising almost the sole constituent of the material that forms the bottom.

From such countless billions of shells were the famous chalk cliffs of England formed. Long ago they were dropped upon the floor of an ancient sea, and were piled so high that those in the undermost layers were squeezed into a shapeless mass; later, by some convulsion of Nature, they were lifted out of the water.

ANIMAL PLANKTON IS ABUNDANT

Minute animal Plankton appears to be as abundant 600 feet deep as at the surface. In this vertical range alone it is estimated that every square mile of salt water contains upward of sixteen tons of planktonic skeletons. And there are innumerable forms that have no shells.

The skeletal structure of some of these creatures, the Foraminifers (see Color Plate VII), is composed of lime; that of others, the Radiolarians (see Color Plate IV), is formed of silica-a transparent, glasslike substance as hard as flint.

Among the Foraminifers, the wellknown genus Globigerina is a representative example. These animals, despite their complex forms, consist of a single cell. They are extremely abundant in warm and temperate seas (see page 304).

The shell consists of successive chambers, usually somewhat spirally arranged, with a mouthlike aperture in the largest chamber, and the entire structure is pierced with numerous fine perforations.

Long, delicate spines of lime radiate from the surface of the chambers, while from the tiny punctures and the shell mouth streams the protoplasm, frothy and latherlike, which lodges between the spines, or extends outward in gauzy threads for the capture of prey. Yet, on occasion, the creature can withdraw completely within its shell.

The arrangement of the spines, which increases the frictional resistance to the water, and the bubbly envelope investing the shell constitute a unique mechanism adapting the animal to a floating life.

Not only are the Globigerina distin