of soil volume, and the degree of compaction during burial, are related to their density or thickness change. Although common sense suggests that volume and density are three dimensional, and thickness it one dimensional, observations on various materials, including fossil plants of known shape (Walton 1936; Briggs and Williams 1981), show that while under conditions of static vertical load, soils and fossils are maintained by pressure at the side. These four simplifying assumptions allow for a detailed analysis of the changes that occur during the formation of a soil and the burial of a soil. (Retallack 2001) In geochemistry, a knowledge of the structure of former soils is also valuable to understand the composition of paleo continents. See also Cutans Paleosols References Subfields of paleontology Pedology