Petrology Petrology Petrology (from the Greek πέτρος, "pétros", "rock" and λόγος, "lógos", "subject matter", see -logy) is the branch of geology that studies rocks and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous and metamorphic petrology are commonly taught together because they both contain heavy use of chemistry, chemical methods, and phase diagrams. Sedimentary petrology is, on the other hand, commonly taught together with stratigraphy because it deals with the processes that form sedimentary rock. Lithology was once approximately synonymous with petrography, but in current usage, lithology focuses on macroscopic hand-sample or outcrop-scale
A Study of History 23 civilizations identified by Toynbee in vol. Vii. This table does not include what Toynbee terms primitive societies, arrested civilizations, or abortive civilizations. Civilizations are shown in boldface. Toynbee's "Universal Churches" are written in "italic" and are chronologically located between second- and third- generation civilizations, as is described in volume VII. The social scientist Ashley Montagu assembled 29 other historians' articles to form a symposium on Toynbee's "A Study of History", published as The book includes three of Toynbee's own essays: "What I am Trying to Do" (originally published in "International Affairs" vol. 31, 1955); "What the Book is For: