Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general a stratum will be primarily igneous or sedimentary relating to how the rock was formed.

Sedimentary layers are laid down by deposition of sediment associated with weathering processes, decaying organic matters (biogenic) or through chemical precipitation. These layers are distinguishable as having many fossils and are important for the study of biostratigraphy. Igneous layers are either plutonic or volcanic in character depending upon the cooling rate of the rock. These layers are generally devoid of fossils and represent intrusions and volcanic activity that occurred over the geologic history of the area.

There are a number of principles that are used to explain the appearance of stratum. When an igneous rock cuts across a formation of sedimentary rock, then we can say that the igneous intrusion is younger than the sedimentary rock. The principle of superposition states that a sedimentary rock layer in a tectonically undisturbed stratum is younger than the one beneath and older than the one above it. The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds.

James Hutton FRSE (Edinburgh, 3 June 1726 OS (14 June 1726 NS) – 26 March 1797) was a Scottish physician, geologist, naturalist, chemical manufacturer and experimental agriculturalist. His work helped to establish the basis of modern geology. His theories of geology and geologic time, also called deep time, came to be included in theories which were called plutonism and uniformitarianism. He is also credited as the first scientist to publicly express the Earth was alive and should be considered a superorganism.

James Hutton was born in Edinburgh on 3 June 1726 OS as one of five children of William Hutton, a merchant who was Edinburgh City Treasurer, but who died in 1729 when James was still young. Hutton's mother - Sarah Balfour - insisted on his education at the High School of Edinburgh where he was particularly interested in mathematics and chemistry, then when he was 14 he attended the University of Edinburgh as a "student of humanity" i.e. Classics (Latin and Greek). He was apprenticed to the lawyer George Chalmers WS when he was 17, but took more interest in chemical experiments than legal work and at the age of 18 became a physician's assistant as well as attending lectures in medicine at the University of Edinburgh. After three years he studied the subject in Paris (University of Paris), then in 1749 took the degree of Doctor of Medicine at Leyden with a thesis on blood circulation. Around 1747 he had a son by a Miss Edington, and though he gave his child James Smeaton Hutton financial assistance, he had little to do with the boy who went on to become a post-office clerk in London.