Slate Formation

the complex of marine sedimentary rocks, deposits of which are characteristic of the early stages of development of geosynclines, primarily of their fringe zones. Slate formation is composed basically of dark argillaceous rock that often has undergone primary metamor-phism and has changed into black, hard, shiny, so-called slate, argillaceous schist—hence, the name of the formation; aleurolith and sandstone, usually graywackes, occupy a secondary place in slate formations. These formations may reach thicknesses of many thousands of meters. Examples of slate formation include rocks of the Lower and Middle Jurassic period of the Greater Caucasus, the Lower Carboniferous period of the Rudnyi Altai, and the Devonian period of the western slopes of the Southern Urals.