Soil basically starts from rock together with decaying animals and plants, if you can imagine the long stretches or periods of time when large rock masses collapsed and broke apart. Heat, the action of water, and friction are largely responsible for this. What is meant by friction here is the friction and grinding of the rock mass against the rock mass.
Think boulders, a perfect mess of them, bumping, scraping, sticking to each other. What was the result? Well, I’m sure you all can work it out. This is what happens: pieces of rock are eroded, lots of heat is generated, pieces of rock are pressed together to form new rock masses, some pieces become water-soluble. Why, myself, almost feel the stress and tension of it all. Can you?
Then, there is also a large temperature change. First everything is heated to a high temperature, then gradually cools down. Just think of the cracks, the collapses, the upheavals that such changes must have caused! You know some of the effects in winter of sudden freezing and thawing. But the small examples of broken water pipes and broken jugs are nothing compared to what was happening in the world at that time. Water and gases in the atmosphere help with this crumbling work.
From all these rubbing actions, which are called mechanical actions, it is quite easy to understand how sand is formed. It is one of the major divisions of sandy soils. The seaside is a large collection of pristine sand. If the soil is just a mass of broken rock, then it will be very poor and unproductive. But early forms of decaying animal and plant life became part of the rock mass and produced better soil. So the soil we call sandy soil has been mixed with sand, other materials, sometimes clay, sometimes vegetables or humus, and often animal waste.
Clay takes us directly to another class of clay. It happens that certain parts of the rock mass become dissolved when water drips on it and heat is abundant and abundant. This dissolution occurs mainly because in the air there is a certain gas called carbon dioxide or carbonic acid gas. These gases attack and change certain substances in the rock. Sometimes you see boulders with parts sticking out as if they have been eaten up.
Carbonic acid does this. It turns this edible part into something else that we call clay. Such changes are not mechanical but chemical. The difference in the two types of change is just this: in the case of sand, where a mechanical change takes place, you still have what you started with, except the size of the mass is smaller. You start with large rocks, and end with small particles of sand. But you don’t have a different kind of stone in the end. The mechanical action can be illustrated with a piece of granulated sugar.
Let the sugar represent a large rock mass. Crush sugar, and even the smallest is sugar. Likewise with rock mass; but in the case of a chemical change you start with one thing and end with another. You start with a large rock mass in which there is a part that is changed by the acid acting on it. It ends up being a completely different thing that we call clay. So in the case of a chemical change something starts with and at the end we have a completely different thing. Clay soils are often called silt soils because of the amount of water used in their formation.
The third type of soil that farmers have to deal with is limestone soil. Remember we are thinking about land from an agricultural point of view. This soil, of course, is usually formed from limestone. As soon as one thing is mentioned about which we know nothing, another emerges which we are just as stupid. And the whole chain of questions follows. Now you are probably saying to yourself, how did limestone first form?
At one time centuries ago the lower forms of animals and plants were taken from the water particles of lime. With chalk they form skeletons or houses about themselves as protection from larger animals. Corals are representatives of this class of skeletal-forming animals.
When the animal dies, the skeleton remains. This great mass of living matter coalesced, after centuries, to form limestone. Some limestones are still shaped in such a way that the shell formations are still visible. Marble, another limestone, is somewhat crystalline in character. Another famous limestone is lime. Maybe you want to know how to always be able to tell limestone. Drop a bit of this acid on some limes. See how it bubbles and sizzles. Then drop some on this chalk as well as on the marble.