Department of Geology
University of Massachusetts
Amherst, Massachusetts 01002
Reprinted from the Proceedings of the First International Conference on the New Basement Tectonics. Utah Geological Association Publication #5, 1976
The methods of "Linesmanship" or the practice of "Linear Geo-Art," evolved in a commonly published class of ancient to recent papers devoted to fracture analysis and related forms of self-delusion
Linear topographic, geologic, or vegetal elements reflecting in some way the bedrock and geomorphic characteristics of an area have long been recognised by geologists. Such pioneering linesmen as W. H. Hobbs (1911) and others began systematic analyses of these linear features to gain widespread recognition and general disbelief by the geologic profession. The advent of the flying machine spawned a prolific new generation of linesmen who demonstrated clearly that by squinting obliquely across air photos a great number of random lines could be drawn.
Satellite imagery has recently impressed a whole new generation of geologists with the potential beauty of the artform. The newcomers have reinvented the line and begun to analyse it in a "scientific manner", unaware of the prior-established rules of Linear Geo-Art and the subtle, sophisticated methods of mutual delusion which generations of linesmen developed before them. With so many new practitioners, a few of them - through accident or design - might corrupt a thing of beauty into something of scientific significance. For the most part, however, the new linesmen need instruction. Accordingly, I have attempted to set down some of the guidelines for the practice of Linesmanship and Linear Geo-Art. The first task is generation of "data", keeping in mind the fundamental rules set forth below:
Given an array of map points, linears can be drawn through any two of them. If two cannot be found, one will suffice. This rule is known to all prospectors who can prove their diggings lie on a straight line with the nearest mine.
In general, it is better to have a reason for drawing a linear. Parallelism to a joint, a fault or another linear is usually reason enough.
No linear ever ends. This is especially true if there is some feature in the next county more or less on its extension which may be construed to be caused by the linear. ("More or Less" means a kilometer or two or three.)
If the feature is slightly off the strike extension of the linear (5 kilometers or more), the linear is obviously incorrect and must be redrawn.
This problem can also be solved by making a wide linear. (Linears with a width greater than their length are considered poor practice.)
Only those linears you personally discover on imagery are real. All others need careful ground checking.
Two linears are "parallel" when they differ by less than 45 degrees in azimuth. (The sqeamish sometimes resort to the term "sub-parallel.")
Parallel linears intersect only in rare circumstances. Where they do is probably a good place for a "buried intrusion."
In other cases, parallel linears cross one another when they are deflected by a major subsurface disturbance. This is probably a reef.
"Orthogonal" linears usually meet at angles somewhat more than 45 degrees. If necessary, "orthogonal" can mean any two linears which intersect. This supports a general observation that most areas are characterized by "orthogonal" patterns of linears. (Care should be used not to apply Rules 7 and 10 simultaneously. "Orthogonal-parallel strains the imagination of even the best linesman.)
Eight fracture directions, each with an uncertainty of 15 degrees, are usually enough to include all linears in "sets". (This eight-fold symmetry has a certain elegance to it, furthermore, and particularly if azimuths are carefully selected so as to parallel wrench faults on the other side of the globe.)
Faced with a linear having an azimuth halfway between two expected directions, competent linesmen can usually curve the feature a bit so as to coincide with one or the other of the two directions. Truly great linesmen can make the linear coincide with both directions. (Use of two different publications is recommended.)
In interpreting linears, remember the first law of tectonics: "Bury it Deep." Failing this, make certain the proposed stresses are "primeval."
Each fracture episode is the first to break an area, keeping in mind the inviolable rule of eternal crustal virginity. This does not cause confusion with the concept of tectonic heredity and its pre-existing influence on fracture directions.
Population density contouring of the number of linears per square kilometer has proven that fewer natural linears are observable in urban areas or over large lakes. Computer processing of linear maps can thus prove useful in locating previously unknown cities and lakes.
In detecting linears, the more sophisticated and expensive the equipment used, the greater significance the linear has.
If you don't know what causes the linear, it must have profound significance.
Any truly great theory for the origin of linears is incapable of proof.