SIEVES like these are used to separate the soil into its various differently sized particles. Soil is made up of many different sized particles from small rocks to sand to silt to clay. Clay particles are very small and are the most important for the chemistry of the soil. The soil in Fargo has a high clay content. This type of clay swells up when it gets wet and shrinks when it dries out. That's why the big cracks form in your yard in the summer and streets are rough.