In order to analyze a macrobotanical assemblage, several steps may be taken. First, charred and waterlogged macrobotanical remains must be separated from soil by a process known as flotation. Mineralized remains and remains from extremely dry contexts can usually be separated from soil and roots with careful dry sieving alone. Although flotation systems differ in size, design, and number of components in order to meet the needs of the assemblage and the restrictions of the site, each system accomplishes the same basic task. Passing water over a soil sample separates the remains into light and heavy fractions. The heavy fraction weighs more than water and, thus, sinks to the bottom and is collected in a screen. The light fraction, which contains the plant remains, floats above the water and is sorted onto another, finer screen. Residual dirt and water are drained out of the unit through an output valve. Light and heavy fractions are then dried to prepare them for analysis.