Stratigraphic columns are illustrations made by geologists to represent the relative composition, thickness and scope of layers of rock, such as in a canyon, a volcano or a cliff. Some drawings are black and white with labeled layers, while others have colors that more closely resemble layers of rock described in the column. Each layer is distinct, and geologists label the general composition of each portion.
Illustrations on stratigraphic columns are standardized so geologists can read each graphic and determine the composition of each layer. Dots represent sandstone. Limestone follows a brick-like pattern. Dolomite is a brick pattern, only with slanted sides. The symbol for broccia looks like irregular spots and blotches. Siltstone looks like broken horizontal lines. Stratigraphic columns for volcanoes or magma chambers are drawn differently because lava doesn't necessarily flow vertically in the same manner as a column does.
Several bits of information are included on stratigraphic columns. The scale of layers, a map or description of the locality, the positions of rock beds, faults or cracks and the methods of measurement are just some keys to stratigraphic columns. A time frame of geologic periods is listed to the side of each illustration.
These illustrations describe any geologic formation with layers. A notable geologic formation illustrated by stratigraphic columns is the Grand Canyon in the United States.