This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
It is from the sedimentary, organic, and igneous rocks that the farmer and gardener obtain the soil in which to grow their crops. When these rocks have been broken down into small particles and mixed in various proportions with organic material, they are capable of yielding up certain foods to plants with a proper supply of moisture and at a certain temperature.
The various rocks have been converted into soil by natural and artificial agencies. Amongst natural agencies the most important are the gases of the atmosphere, water (including rain, rivers, streams), wind, heat and cold (frost and snow), and vegetation. Amongst what may be called artificial agencies are the cultural operations of man - ploughing, digging, hoeing, harrowing, and manuring.
The natural agencies may be embraced in one word, "weathering", and the cultivator should impress upon his mind what important and powerful friends he has in them. The action of the weather - rain, frost, snow, sunshine, wind - never ceases; it is wearing away the face of the hardest rocks and flints, as well as the surfaces of cultivated soils, both day and night, and bringing them into a more fertile condition. This important work costs nothing, but how many realize that it is always going on!
It may be as well to consider the individual action of each of the natural agents.