The bearing capacity of soil is an important consideration in construction projects. The bearing capacity of soil is the pressure that a soil sample can withstand without collapsing. The bearing capacity varies depending on the cohesion of the soil. Cohesion is the force that holds molecules and particles inside the soil together. Rock is a continuous mass of solid mineral material, such as granite or limestone, that can only be removed by drilling or blasting. The rock is never completely formed into a single large segment, but is crossed by a system of joints which divides it into irregular blocks. Despite these joints, rock is generally considered the strongest and most stable material on which a building can be founded. Soil is a general term for earth material made up of particles. If an individual piece of earth is too large to be lifted by one hand, it is considered a rock. Although it takes your whole hand to lift a particle, it is still a pebble. If a particle can be lifted without difficulty with the thumb and forefinger, the soil is classified as gravel. If individual particles can be seen but are too small to pick up individually, the soil is called sand. Sand and gravel are coarse-grained soils, meaning at least half of the material is retained on a number 200 sieve. Peat, topsoil, and other organic soils are unreliable for supporting foundations of buildings. Due to their high concentration of organic matter, they are spongy and compress easily. Their properties may change over time due to changes in soil water content or biological activity. Clay soils are generally considered very cohesive because they retain measurable shear strength (an ability of materials to resist forces that can cause a soil's internal structure). material to slide against itself), in the absence of confining forces. The ability of loose or frictional soil, such as sand or silt, to support a building depends on the friction between its particles. Sand confined by the surrounding soil in the earth can support a heavy building, whereas a conical pile of sand on the earth's surface cannot support anything, because there is little or no shear resistance between the particles. Beneath each stope are a number of superimposed layers, also called strata, of different soils. In ancient times, the actions of natural forces allowed layers to be deposited on top of each other...