Definitions

Thickness: the perpendicular distance between the parallel planes bounding a tabular body, as displayed on any section perpendicular to these planes; also called the true or stratigraphic thickness (Fig. 2.1).

Apparent thickness: the distance between the bounding planes measured in some other direction, for example, the perpendicular distance between the traces of the bounding planes on an oblique section, or in some other specified direction, as in a drill hole. It is always greater than true thickness.

Outcrop width: the strike-normal distance between the traces of the parallel bounding planes measured at the earth's surface. It may be measured horizontally or on an incline.

Depth: the vertical distance from a specified level (commonly the earth's surface) downward to a point, line or plane.

Thickness determination

Although geologists may determine the thickness of any stratiform body of rock, most often the concern is with the thickness of layers of sedimentary rocks. In this context “measuring a section” generally refers to a lithologic description of the rock strata as well as a determination of their thicknesses (Kottlowski, 1965; Compton, 1985). Here, the concern is with thickness alone. The thickness of a layer may be determined in a number of ways. In special circumstances it may be possible to measure it directly, otherwise it must be determined from indirect measurements.