A formation is a set of similar beds , and formations are the fundamental units of stratigraphy . Distinct and different from adjacent rock units above and below. Formations must have names . Formations are usually named for some geographic locality where they are particularly well exposed. If the beds are dominated by a single rock type, this may appear in the name.
Members also have names.
A formation, however, does not have to contain members. Intrusive and highly deformed and metamorphosed rocks are called lithodemic units . Unfortunately, a lot of mapping in the Piedmont predates this code, and many of the units on the available maps are referred to as formations. In this lab, we are primarily concerned with sequences of sedimentary rocks and occasional lava flows, so we will be using lithostratigraphic terminology. Using these data, the geologist draws up a stratigraphic section for a particular sequence of rock.