Abstract

The terms “lineaments,” “linears,” “linear trends,” “linear features,” “lineations,” “fractures,” “fracture traces,” “megojoints,” “vincula,” and “photogeophysics” appear in the geologic literature with increasing frequency. The definitions of these forms, however, are loose, contradictory, and sometimes misleading. Some of these terms are applied indiscriminately and qualitatively, semi-quantitatively, or quantitatively to features which range from local to regional to super-regional in scale. The methods used to detect linear features range from the study of aerial photographs and physiographic maps to field and microscopic observations.

It is proposed that the term “lineation” be used as a descriptive and nongenetic term for a natural linear feature of any length which is either exposed or partly covered by surficial material. Lineations include megalineaments (> 100 km), lineaments (10 km to 100 km), macro-linears (2 km to < 10 km), brachylinears (lower limit of visibility of unaided eye in the field to < 2 km), and microlinears (microscopic).

Because of the wide application of aerial photographs, it is proposed that when aerial photographs are the medium of study, the term “lineation” be qualified by the term “air photo.” The term “air photo lineation” is thus a descriptive and nongenetic term for any linear feature of any length encompassing topographic, physiographic (including straight stream segments), lithologic, structural, vegetative, or soil tonal alignment or any combination thereof, visible primarily on aerial photographs or on composite mosaic and index aerial photographs. The same length subdivisions proposed for lineations are also proposed for air photo lineations.

It is recommended that the terms “fracture trace,” “megajoints,” “vincula,” and “photogeophysics” be dropped to avoid confusion or redundancy.

The terms “set,” “system,” and “pattern” may be used to describe linear features as they are commonly understood in structural geology.