How Soil Is Made And Carried
( Originally Published 1891 )
"See the brooklets flowing,
" Yet to help their giving,
- ADELAIDE A. PROCTER.
"AH! it has been raining," thought Bunny, as he peeped from his burrow to see the sunrise.
"How the water has worn the hillside ! See the little valleys it has made. It must have rained very hard. I will call for Dick and Chip, and then hurry down to the brook. What a wonderful story it will have to tell this morning."
"How muddy you are, little stream," whispered the wild-flower, as it shook the raindrops from its pretty head.
"And how wide!" chirped Redbreast. "But here come our friends down the hillside, and now we can hear the brooklet's story."
0 tell us, please, where all this muddy water comes from," were the first words of the chipmonk. " What will you ever do with it ? You are not nearly so pretty as you were yesterday."
" When I have told you my story, Chip, you may think that I am much prettier with my dark load than when I was a clear stream..
"Last night a heavy shower fell in our valley. The hillsides were covered with tiny streams that chased each other down the slopes like playful squirrels.
"But my little rills were hard at work. You should have seen them roll the pebbles, down the bluffs, and break off the sharp edges. Then they washed the sand together, and rounded its corners.
They wore deep gullies in the steep places, and carried away the finest soil. They swept the light loam down the slopes. They ran away with the pretty earthworm mounds and tiny ant-hills. They spread the rich soil all over the meadow, and some of it they even brought to me. That is why I am so muddy this morning.
"0, my little rills were not lazy last night !
"But the work is not yet done, as you will see. I am flowing towards the rapids, and will soon be in the pond. I want you all to follow and see what becomes of my load of silt, or fine rich soil. You may also throw some sand and pebbles into the rapids, and then watch closely."
Bunny and Dick scraped some gravel from the bank, and it fell into the water just where it rushed over the steep place in the brook-bed.
" How muddy it is ! " chirped the robin. "We cannot see the bottom."
"Look here!" shouted Dick. "The pebbles have all sunk in the rapids. Some are rolling down the steep bed. The rushing water must be moving them there."
"And here is the sand below the rapids! " cried Chip. It is spreading over the bed of the brook like a great oak-leaf."
"Perhaps the stream cannot carry it any farther," said Bunny. " In the pool just below the rapids, the water moves very slowly."
"Here goes the black loam ! " piped Redbreast. "It is flowing into the pond now."
They all ran quickly to the spot, and surely enough, there it was in the still water.
"Watch closely ! " bubbled the brook.
" The silt is settling now," said sharp-eyed Chip. " The bed of the pond, near where the stream flows in, is nearly black. 0 see ! it is making a bank of soil there ! "
" Why doesn't it spread all over the bed of the pond, Dick ? " asked the robin.
" It may be because the water flows very slowly, and must now lay down its fine soil, just as it dropped its sand near the foot of the rapids," was the gray squirrel's answer.
" You are right, Dick," rippled the brook." I must leave nearly all of my silt here. I can carry it no farther. It is not the current, or forward motion, that keeps the sediment from settling higher up the stream. It is the rolling, mixing motion of the water.
"All day long I shall pour this rich loam into the pond, and build the muddy bed higher and higher.
" Now, my little companions, you know how all the brooks in the world are at work,— yes, and the tiny rills and large rivers. They are all doing just what you have seen me do to-day.
" They are wearing down the slopes, grinding the pebbles and sand into fine soil, and carrying their rich loads down to the lowlands. Grain by grain, the hills are covering the valleys, for it is the work of water to wear down the highlands, and fill in all the low places, so that the land will slope evenly from the water-partings to the sea.
" If you will look about, you will see many places where the streams have been at work. All along the foot of the bluffs, there are large stones that have rolled down the steep slopes, after the rills have washed the fine sand and loam from around them. You will also find them along the shore, where they have dropped from the banks.
" When I was here many years ago, the bluffs were much nearer than now. But we have worn them away a little during every rainstorm, and my little rills will work on to try to make the hills level with the meadow.
Now look once more at the mud-banks forming in the pond. They are made of the richest soil in our valley. The water is very high now, but when it has settled, you will find little islands where the silt-beds are.
" When it rains again, I shall bring down more soil, and make the muddy bank still wider on the pond-bed. After a long time, the little shallow place will be filled with loam, and then there will be no pond, but another fertile spot in the meadow. The green place above the rapids shows where there was once a pretty pond that has been filled in this way.
"The islands that you see growing are called a delta.' In the mouths of great rivers, deltas often form so large that cities are built upon them. Some are also covered with grain fields and forests. Deltas are made by all muddy streams that flow into ponds, lakes, seas, or any bodies of water that have but little motion. Of course they cannot grow in water that runs swiftly, because the silt is swept away and cannot settle.
" You must not think that a delta is the only place where a stream deposits its rich load. All over the valley, in every nook and corner, the rain-drops and rills spread the fine soil. But they sweep the greater part into the lowlands.
"Wherever the water eddies into little bays and becomes calm, you will find a dark muddy bottom. There you will also see the water-plants growing. All up and down my shores, behind nearly every bend in my course, along every part of the banks where the current is weak, the fertile land is forming.
" But my greatest work is done along the beds of the tiny rills that spring into life only during a rainstorm. Wee little streams they are, trickling down every part of the slopes, — so small that, even the tufts of grass and rounded pebbles turn them aside. They flow into every crack and crevice all over the slanting sides of our valley, and spread a feast of the finest and richest soil for the plants. Every time it rains the work goes on."
" But what becomes of the rills when the storm is over ? " asked Bunny.
"A part of their water sinks into the earth, and forms underground rills that feed the springs ; some creeps into the roots and seeds ; some runs down the surface of the slopes and carries soil to the brooks ; and some is taken away by the sunbeams.
" You can see a picture of these tiny rills if you will look closely at the upper surface of a large maple-leaf. The finest, network that you can find will show how the rills cover the slopes during a heavy shower ; and just as these hair-veins all lead to the great mid-vein of the leaf, so the rills all run together down the slopes, becoming larger and larger as more of them are joined, till they unite with the mid-stream of our valley, — the brook that flows along the line of lowest levels.
Little by little the rills wear away the slopes each year, and help to lower the surface of the highlands.
There are also our cascades and rapids, where the beds are steep and are often rapidly worn away. Sometimes the melting snow makes torrents in the narrow gullies on the hillsides. The rushing water will then sweep large stones and coarse gravel into the meadows, except where the trees and bushes check the flow of the water and stop the rolling stones.
" There were no torrents in our valley years ago, when the surface was covered with trees. Only about one-half as much rain fell on the ground then as now, because so much was taken in by the bark and leaves. A great deal also followed the tree-trunks into the soil.
" Then, too, in winter the snow that lay in the forest melted very slowly, because the warm sun-beams could not reach it so easily, and strong winds could not sweep over the drifts and scatter the flakes through the air.
In those days the streams flowed more evenly than now. During the rainy season they rose a little, and then fell slightly while the dry months lasted. But they were never without water.
"Now when heavy rain falls, or snow melts, the banks cannot hold all the water that rushes down the slopes. But after weeks pass without rain, and the fields are brown and bare, the brook becomes only a series of muddy pools. Sometimes its bed dries and cracks under the hot sun, and not a drop of water can be found in it.
"What you have seen to-day, little friends, tells the story of how soil is being made and carried, not only in millions of brook valleys all over the earth, but also in the vast river basins.
" Remember that the finest loam is carried farthest, and that it does not settle till the water is almost still. Then you will know why the highland has coarser soil than the meadow, and why the steep slope cannot produce like the more level lowland.
" It is the same everywhere, — in the valley of the tiniest rill on our hillside, and in the basin of the mighty Amazon. Now I will tell you the story I promised about the Nile at work in the desert :
" Once more we will visit the high mountains. The snow of winter is just melting. Hundreds of little streams rush and foam down the steep slopes.
" It is early morning, and a bright star shines above the first gray tints in the east. It is the 'Dog Star,' and how happy the ,poor people in the valley are to see it, for now the dry banks of the Nile will — but I am ahead of my story.
" Let us watch the foaming streams as they flow into the great river. It seems as if its banks can hold no more. How the old stream roars as it tears over the rapids ! What will become of the flood that is sweeping into the valley ?
" Let us follow ! Now we can see the parched banks once more. The sun is nearly overhead. How hot and dry the air feels ! 0, if it would only rain !
" But look ! The river still rises, — higher and higher. Now it creeps slowly over its banks ! Where will it stop? What will become of the poor people ?
" See ! they are shouting and dancing for joy What can it mean ?
" Wider and wider flows the stream. The dry fields are covered. We look for the river. It is gone. In its place is a long, wide lake.
"Still it spreads, — wider and wider. Will it never stop ? June passes. The July sun beats down. Yet the water rises. August is here, and now the whole valley is covered by the wonderful stream.
" At length the water begins to go back. Day after day it settles. September comes and goes and if we were there on this bright October morning, we should see only the muddy river, flowing in its old bed once more.
"We look again for the dry banks and the desert. They are not there. Everything is changed. For miles on both sides, the water has covered the valley with rich soil.
" Now we know why the people were shouting and dancing. The land is ready for their seeds ; and soon the golden grain will wave all over the valley. There will be food for the next long, dry season.
" Every year this wonderful river overflows its banks when the Dog Star rises in the early morning. Then the heavy rainfall around its sources, and the melting snow on the mountains, send down the flood to spread the soil over the parched valley.
" The slopes supply the food for plants, and the water carries it down in that great river just as in our little brook. That is why I am so muddy today.
" Now good by till tomorrow."
Just then little Chip ran down, and whispered something to the brook. What do you think it was he said ? Then he scampered away to the old oak just as fast as his little legs could carry him.