Lineament, linear, lineation: Some proposed new standards for old terms D. W. O'LEARY J. D. FRIEDMAN [ U.S. Geological Survey, Federal Center, Denver, Colorado 80225 H. A. POHN ABSTRACT ORIGIN OF TERMS The words "lineament," "linear," and "lineation" have become Lineament increasingly popular since the advent of spacecraft and high- altitude aircraft images. With the increased usage has come a con- The word "lineament" was introduced by Hobbs (1904) to comitant relaxation in the definitions of these terms, until the liter- characterize the spatial relationships of landscape features that in- ature now is overwhelmed with conflicting and equivocal mean- cluded (p. 485) "(1) crests of ridges or boundaries of elevated areas, ings. The need for clarification of these terms is clear. We propose a (2) the drainage lines, (3) coast lines, and (4) boundary lines of return to more fundamental conceptual definitions, based on origi- formations, of petrographic rock types, or of lines of outcrops." In nal usage. We define the word "lineament" in an essentially a later publication (1912), he added to these features ravines or val- geomorphological sense, on the basis of the usage introduced by leys and visible lines of fracture or zones of fault breccia. According Hobbs: A lineament is a mappable, simple or composite linear fea- to Hobbs, any number of these features may be joined end to end to ture of a surface, whose parts are aligned in a rectilinear or slightly constitute a lineament. He pointed out (1904, p. 485, footnote) curvilinear relationship and which differs distinctly from the pat- that lineaments are not equivalent to the "tektonische linien" of terns of adjacent features and presumably reflects a subsurface German writers, "as these are mostly regarded as lines of displace- phenomenon. The word "linear" is restricted to its original adjecti- ment." Hobbs felt that by attaching this meaning the term would val sense to avoid the increasingly popular but grammatically and be too restrictive. However, in 1912 (p. 227) he added a strong tec- conceptually incorrect nominative use. The word "lineation" is re- tonic implication to his definition by stating: "Many lineaments are stored to its fundamental petrographic meaning: lineation is the identical with seismotectonic lines and they therefore afford a one-dimensional structural alignment of internal components of a means of to some extent determining in advance the lines of rock, is imposed by external agents, and cannot be depicted as an greatest danger from earthquake shock." His actual definitions of individual feature on a map. In addition, we suggest usages of lineament are broad and metaphorical: "... significant lines of "line" and "alignment" to refer to nongeologic features and (or) landscape which reveal the hidden architecture of the rock base- questionable features that do not fit proposed criteria and where ment are described as lineaments" (1912, p. 227); "the term as here definitional restrictions or implications may be a problem. used is nothing more than a generally rectilinear earth feature" (1904, p. 485); ". they are the character lines of the earth's INTRODUCTION physiognomy" (1912, p. 227). However, his parenthetical notes give a better idea of what he had in mind. He pointed out (1904) Lineament, linear, lineation: what do these words mean and how that the linear aspect of lineaments is scale related: ". lineaments and why are they used? This question is pertinent in the face of a which may appear rectilinear on maps, may be so only in propor- growing number of studies in remote sensing, where much is made tion as the scale of the map is small" (p. 486). Lineaments "must be of the significance of linear features but where the drawbacks of conceived to outline in the majority of instances a complex but conflicting terminology have become increasingly apparent. There comparatively narrow zone of displacements, in which other direc- is often little agreement as to what linear features are because tions than that given by the general trend are included" (p. 486). criteria for recognition are not clearly established and because He also pointed out (1912, p. 227) the composite nature of linea- definitions are poor or inadequate. ments: "It is important to emphasize the essentially composite ex- The present state of confusion is underscored by the American pression of the lineament, but in every case it is some surface ex- Geological Institute's Glossary of Geology (Gary and others, pression of a buried feature." 1972, p. 408), where lineament is defined in three contexts: lunar, Following the reasonably clear and explicit definitions of Hobbs, photogeologic, and tectonic. The divergence of meaning implicit in a host of more or less divergent definitions have been proposed up the three separate entries, in addition to the nominative use of to the present day. These are listed chronologically in Table 1. linear as a synonym for tectonic lineament, illustrates the confused status of these terms and the lack of unequivocal definitions. These Linear terms need to be reappraised, not only to serve new insights and new applications based on remote sensor images, but also to The nominative use of the word "linear" has a relatively short achieve consistency between descriptions based on images and history. Sonder (1938) used the term to refer to individual features photos and descriptions based on field data. Our aim in this paper which Hobbs called lineaments; he proposed also that lineament be is to analyze the use of these terms and to propose conceptual used in a general, regional sense (p. 223, 225): "The lineament of a definitions and objective criteria for them. region then denotes a definite direction which is contained in the Geological Society of America Bulletin, v. 87, p. 1463-1469, October 1976, Doc. no. 61011. 1463 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/10/1463/3433659/i0016-7606-87-10-1463.pdf by guest on 24 September 2021 1464 O'LEARY AND OTHERS tectonics, the jointing, and the relief." Gross (1951) elaborated this (p. 77): "The broken and sheared rock of a fault generally erodes concept and eliminated the term lineament altogether. He used the more rapidly than the solid rocks adjoining, and as a result faults word lineation to implicitly refer to the general trend of "linears," often occur in elongated topographic depressions called linears." as Sonder had used the word lineament: "The topographic linea- tion in any given direction may have any one of a number of causes Lineation and ... in general, it is folly to draw structural conclusions from a study of physiography alone" (p. 87). However, he did draw such Anderson (1915) first used the term "lineation," which he conclusions, and in doing so he seemed to confuse cause and effect defined (p. 22) as "a sort of striation visible on practically any TABLE 1. REPRESENTATIVE GEOLOGIC USAGE OF TERMS "LINEAMENT" AND "LINEAR," 1904-1973 Reference Definition Comment Hobbs (1904) A lineament is "nothing more than a generally rectilinear Term introduced to characterize spatial relationships of "1) earth feature" (p. 485) crests of ridges or boundaries of elevated areas, 2) drain- age lines, 3) coast lines, 4) boundary lines of formations, or petrographic rock types, or lines of outcrops" (p. 485). Any of these may be joined end to end. Term is scale related: "lineaments . (are) rectilinear . only in pro- portion as the scale of the map is small" (p. 486). Line- aments tend to be obscure Hobbs (1912) Lineaments are "significant lines of landscape which re- Features include ravines, valleys, and visible lines of fracture veal the hidden architecture of the rock basement (p. or fault breccia zones but are in every case some surface 227); "the character lines of the earth's physiognomy" expression of a buried feature. Many are equivalent to (p. 227) "seismotectonic lines." They are composite features Sonder (1938) "The lineament of a region then denotes a definite direc- Used in a general, regional sense; individual features (com- tion which is contained in the tectonics, the jointing, pare Hobbs, 1904, 1912) are termed "linears" and the relief" (p. 223) Wilson (1941) Lineaments are "straight and gently curving lines" Emphasized structure: "Their association in definite pat- formed by "the great scarps and troughs which cross terns strongly suggests that they are members of con- all the Precambrian rocks" (p. 496) nected systems of faulting" (p. 496). Described as regional features better seen in air photos than on ground "A lineament is a straight linear surface feature that is "Lineaments are well shown on aerial photographs and . Kaiser (1950) at least many hundreds of feet and commonly many may consist of 1) linear topographic features, either miles long" (p. 1475) trenches or ridges; 2) linear vegetation patterns; 3) linear patterns of soil color or texture. Gaps and steam segments typically form parts of lineaments" (p. 1475) "The straight line or gently curved physiographic fea- "Linears" generally fault related; synonyms are "topo- Gross (1951) tures on the earth's surface are known as linears" (p. 79) graphic linear" and "lineal topographic feature." Used "lineal" as adjectival substitute for "linear." Used "lineation" to refer implicitly to general trend of linears (compare Sonder, 1938) 'In general terms a lineament is a rectilinear feature of Lineaments are usually "interrupted or discontinuous Kelly (1955) considerable extent on the surface of the earth. A tec- features" not readily mapped in the field and are "agree- tonic lineament . [is] either a general alignment of ments of boundary or line observed generally on regional structural features or a boundary between contrasting maps" (p. 58). Term is usually reserved for "transverse or structural features" (p. 58) oblique alignments of one sort or another" (p. 58), but included "in the broadest sense" (p.