The Adventures of a Grain of Dust Part 5

And what muscles Jack has! Freezing water exerts a pressure of 138 tons to the square foot; so there's no holding out against him once he gets his ice wedges in a good crack. He sends huge blocks tumbling down the mountainside. The larger blocks, striking against one another, break off smaller fragments. The smallest fragments the wind seizes. Others are washed down by the rains. The largest, carried away by mountain torrents, b.u.mp together as they thunder along, and so break off more fragments and grind them so small that the wind can pick them up along the banks when the torrents shrink, or in their beds when these sudden streams go dry.

RUNNING WATER AND THE WINDS

In changing rock into soil, running water and the winds each have an advantage over the other. Water weighs a great deal more than air--over 800 times as much--and so grinds faster with its tools of pebbles and sand. The winds, on the other hand, get over a great deal more territory, and they, like the lichens, understand chemistry. Two of the gases they always carry right with them--carbon dioxide and oxygen--help decay the rocks.

As I said, the winds do most work in dry and desert regions, but when you remember that over a fifth of the globe is just that--dry as a bone most of the time--you see this is a great field. It has been so from the beginning, for it is thought probable that there was always about the same proportion of desert lands. Night and day the winds have been busy through all these ages. Dust is carried up by ascending air currents.

Then the same force that keeps the earth in its...o...b..t--gravity--pulls down on a grain of dust. But its fall is checked by the friction of the air. You see there's a lot of mechanics involved in moving a grain of dust; and Nature goes about it as if it were the most serious business in the world; handles every grain as if the future of the universe depended on it. In the case of sand or coa.r.s.e dust, unless the winds are very strong, gravity soon gets the best of it, and down the dust grain comes to the ground again; then up with another current, then down again--carried far by stiff breezes, only a short distance by puffs--a kind of hop, skip, and jump. But fine dust getting a good lift into the upper currents at the start may stay in the air for weeks.

[Ill.u.s.tration: _Courtesy of The Dunham Company._

TO KEEP MOISTURE AND SOIL AT HOME

In the broad fields of the West, where "dry-farming" is practised, they have these huge machines. They are called "Cultipackers." They are cultivators with big, broad-brimmed wheels that pack the surface of the soil after the blades of the cultivator have stirred it. This not only prevents the moisture in the soil from evaporating as fast as it would otherwise do, but keeps the winds from carrying away the soil itself.]

In very wild wind-storms it has been figured out that there may be as much as 126,000 tons of dust per cubic mile; several good farms in the air at once, over every square mile of the earth below!

III. THE STORM PLOUGHS OF THE WIND

TWO KINDS OF WOODEN PLOUGHS

They use wooden ploughs, these winds, just as primitive man did, and as primitive peoples do now; but not quite in the same way, and the ploughing they do is much better. For man's wooden plough is a crooked stick made from the branches of a tree while the winds use the whole tree--roots and all, and both on mountainsides and on level lands the amount of ploughing they do is immense.

Almost all forests are liable to occasional hurricanes which lay the trees over thousands of acres in one immense swath. A large number of these trees, owing to their strong trunks, do not break off but uproot, lifting great sheets of earth. Soon, by the action of its own weight and the elements, this soil falls back. The depth to which this natural ploughing is done depends, of course, on the character of the tree, but as it is the older and larger trees that are most likely to be overturned, since they spread more surface to the wind, the ploughing is much deeper than men do with ordinary ploughs.

The result is that new unused soil is constantly being brought to the surface; and not only this, but air is introduced into the soil far below the point reached by ordinary ploughing. The soil needs air just as we do; for the air hurries the decay of the soil and its preparation for the uses of the plant. The immediate purpose of ploughing is to loosen the soil so that the roots of the plants can get their food and air more easily. It also helps to keep the fields fertile by exposing the lower soil to more rapid decay.

But here's the trouble: While the ordinary plough introduces air into the soil for a few inches from the surface, the subsoil, which is very important to the prosperity of the plant, is practically left out of it, so far as getting needed fresh air is concerned. The long roots of the trees that, among other things opened for it channels to the air, are gone. The burrowing animals that used to loosen up the earth, man has driven away. More than that, the foot of the plough which has to press heavily on the subsoil in order to turn the furrow, smears and compacts the earth into a hard layer, which shuts out the air, and also--to a certain extent--the water from the lower levels.

[Ill.u.s.tration: HOW THE SOIL GETS ITS BREATH

Plants must have air to breathe, both above and below the soil, and the microscope is showing us here how a sandy loam allows the air to reach the roots.]

In mountain regions these "storm ploughs," as we may call them, not only help to renew and prepare the soil in the valleys, but are a part of the machinery of delivery of new soil from mountain to valley. When trees on the mountainside are overturned, they not only bring up the soil, which the mountain rains quickly carry to the valleys, but the roots having penetrated--as they always do--into the crevices of the rocks, bring up stones already partly decayed by the acids of the roots. These stones, as the roots die, decay and so release their hold, and also go tumbling down toward the valley.

Consider how much of this storm-ploughing must be done in the forests of the world in a single year, and that this has been going on ever since trees grew big on the face of the earth. In a storm in the woods of California, Muir heard trees falling at the rate of one every two or three minutes. And, as I said, it is precisely the trees that can do the most ploughing--the older and larger trees--that are most apt to go down before the wind. Younger trees will bend while older and stiffer trees hold on to the last. Before a mountain gale, pines, six feet in diameter, will bend like gra.s.s. But when the roots, long and strong as they are, can no longer resist the prying of the mighty lever--the trunk with its limbs and branches--swaying in the winds, down go the old giants with crashes that shake the hills. After a violent gale the ground is covered thick with fallen trunks[7] that lie crossed like storm-lodged wheat.

[7] Muir: "Mountains of California."

There are two trees, however, Muir says, that are never blown down so long as they continue in good health. These are the juniper and dwarf pine of the summit peaks.

"Their stout, crooked roots grip the storm-beaten ledges like eagle's claws, while their lithe, cord-like branches bend round completely, offering but slight holds for winds, however violent."

AT THE STORM FESTIVAL WITH MR. MUIR

Trees were among Muir's best friends, and he spent a large part of his life chumming with them. What do you think that man did once? He was always doing such things. He climbed a tree in a terrific gale so that he could see right into the heart of the storm and watch everything that was going on. Just hear him tell about it:

"After cautiously casting about I made choice of the tallest of a group of Douglas spruces that were growing close together like a tuft of gra.s.s, no one of which seemed likely to fall unless the rest fell with it. Being accustomed to climb trees in making botanical studies, I experienced no difficulty in reaching the top of this one, and never before did I enjoy so n.o.ble an exhilaration of motion."

And such odors! These winds had come all the way from the sea, over beds of flowers in the mountain meadows of the Sierras; then across the plains and up the foot-hills and into the piny woods "with all the varied incense gathered by the way."

[Ill.u.s.tration: THREE KINDS OF SEED THAT THE WIND SHAKES FREE

Here are three kinds of seed adapted for dispersal by the shaking action of the wind.]

Though comparatively young, these trees--the one Mr. Muir climbed into and its neighbors--were about 100 feet high, and "their lithe, brushy tops were rocking and swirling in wild ecstasy." In its greatest sweeps the top of Muir's tree described an arc of from twenty to thirty degrees, but he felt sure it wouldn't break, and so he proceeded to take in the great storm show.

"Now my eye roved over the piny hills and dales as over fields of waving grain, and felt the light running in ripples across the valleys from ridge to ridge, as the shining foliage was stirred by the waves of air. Oftentimes these waves of reflected light would break up suddenly into a kind of beaten foam and finally disappear on some hillside, like sea waves on a shelving sh.o.r.e."

This was his impression of the forest as a whole, a dark green sea of tossing waves. But if we study trees as long and lovingly as Muir did, we can pick out the different members of the family a mile away--even several miles away--by their gestures, their style of grave and graceful dancing in the wind.

[Ill.u.s.tration: TYPES OF FLYING MACHINE

Here is the type of flying machine that carries men. On the opposite page is the kind that carries the dandelion seeds.]

[Ill.u.s.tration: THE DANDELION-SEED FLYING MACHINE

The dandelion on the left shows how the seeds are kept in the "hangar"

at night and on rainy days, shut up tight to prevent them from getting wet with rain or dew and so made unfit for flying.]

Muir especially mentions the sugar-pines as interpreting that storm to him. They seemed to be roused by the wildest bursts of the wind music to a "pa.s.sionate exhilaration," as if saying "_Oh_, what a glorious day this is!"

This was the picture part of it--the glorious moving-picture show. Now listen to some of the music:

"The sounds of the storm corresponded gloriously with the wild exuberance of light and motion. The profound ba.s.s of the naked branches and boles booming like waterfalls, the quick, tense vibrations of the pine-needles, now rising to a shrill, whistling hiss, now falling to a silky murmur. The rustling of laurel groves in the dells, and the keen metallic click of leaf on leaf--all this was heard in easy a.n.a.lysis when the attention was calmly bent.

"Even when the grand anthem had swelled to its highest pitch I could distinctly hear the varying tones of individual trees--spruce, fir, pine, and oak--and even the infinitely gentle rustle of the withered gra.s.ses at my feet."

When the winds began to fall and the sky to clear, Muir climbed down and made his way back home.

"The storm tones died away, and turning toward the east I beheld the countless hosts of the forests hushed and tranquil, towering above one another on the slopes of the hills like a devout audience. The setting sun filled them with amber light, and seemed to say while they listened:

"'My peace I give unto you.'"

HIDE AND SEEK IN THE LIBRARY

Did you know that the ash and maple seeds actually have screw propellers, like a ship, so that they can ride on the wind?

Pettigrew's great work, "Design in Nature," makes this very plain, both in word and picture.

In what way does the wind help to _produce_ the seed of gra.s.ses as well as carry and plant them? (Any encyclopaedia or botany will tell you how plants are fertilized.)

How could a tempest that blew down a tree help its seeds to get a start? Wallace, in his "World of Life," says that on a full-grown oak or beech there may be 100,000 seeds that are thus given a better chance of life.

Speaking of "wind ploughs," what is the object of ploughing anyway?

The article on preparing the seed bed in "The Country Life Reader"