a branch of geology that studies the history and principles of the development of the earth’s crust and of the earth as a whole. Its main tasks are reconstructing and interpreting theoretically the evolution of the earth’s surface and the organic world that populates it and clarifying the history of the transformation of the internal structure of the earth’s crust and the development of endogenic processes connected with this transformation.

Historical geology relies on the conclusions from particular geological sciences. Its basis is stratigraphy, which establishes the order in which rocks were formed in terms of time and works out a system of chronology for the geological past. One of the main subdivisions of stratigraphy is biostratigraphy, which uses the fossils of extinct animals and plants as indexes of the relative age of rock and which is closely linked to paleontology. Along with relative geochronology, absolute geochronology is developing, making it possible to determine the absolute age of rocks directly.

Constructing a system of geological chronology is an essential prerequisite for historical geological research proper, whose main content is a re-creation of the chronicle of the varied exogenic and endogenic processes that have occurred on the surface and in the interior of the earth in the past.

The task of paleogeography is the reconstruction of these processes and of the physicogeographical conditions in which they occurred, including the distribution of land and sea, the depth and characteristics of the hydrological regime of marine bodies of water, the relief and climate, and the distribution of organisms and their communities.

Historical geology also studies the history of the formation of the structure of the earth’s crust (historical geotectonics), inasmuch as movements and tectonic deformations of the crust are the most important factors in most changes that have occurred on the earth. In questions concerning the development of deep-seated magmatism, volcanism, and metamorphism, which are related to deformations of the earth’s crust, historical geology is closely allied to genetic petrography. Especially important for historical geology is the theory of formation in time succession of natural associations (parageneses) of rocks, which in their composition and structure reflect the complex interaction of various processes that have occurred in the past.

Stratigraphy, which took shape as an independent discipline in the early 19th century when W. Smith in Great Britain and G. Cuvier and A. Brongniart in France laid the foundations of the biostratigraphic method, developed earlier than the other subdivisions of historical geology. This made it possible to work out the main features of the scale of relative geochronology by the mid-19th century. Cuvier developed the concept of catas-trophism. In the mid-19th century, as a result of the triumph of C. Lyell’s uniformitarian ideas, there was a rejection of the catastrophic concept in historical geology, and the idea of the continuous and gradual transformation of the earth’s face took root. In the second half of the 19th century, after the appearance of C. Darwin’s works, the evolutionary theory entered geology. The formation of modern historical geology as a science also dates to this period.

Historical geology has identified the basic principles of the development of geological processes (the emergence and transformation of geosynclines and platforms, the formation of continents, change in the nature of magmatism in the history of the earth, and so on) and outlined the general direction of the development of the earth’s crust and the development of the planet as a whole.