Linear Patterns

Abstract

A rocky surface of appreciable extent, be it examined in a mine, a quarry or a natural exposure, generally reveals two or more systems of dislocations. Sometines these are mere joints (diaclases) along which the rock opens up under the hammer of the geologist. Elsewhere fissures may be seen, seldom open, sometimes filled up by minerals or ore-deposits that condensed from exhalations or hot solutions. Apart from these features, the geological explorer frequently comes across localities showing unmistakable evidence of displacement along prevailing fracture-planes. The origin of these tectonic elements may be very different and may vary according to several local circumstances. The orientation of the joints and fissures may be a question of cleavage due to special localised regional circumstances of pressure or tension. It is a well-known fact that granite batholiths and other plutonic bodies have their characteristic joint-systems, the prevailing directions of joints depending on the stress caused by the shape of the surrounding walls and the load of the strata that originally covered it. A special kind of jointing originates in a cooling lava flow. Striking dislocations are associated with folded mountain-chains and their foreland. And it is obvious that older high-situated rock masses or “massifs” exert a marked influence on the direction of the faults that formed in their surroundings.

“Partout, même dans les pays où les couches ont conservé a peu près leur horizontalité, les formes du sol offrent le reflet d’innombrables cassures internes qui s’y répercutent en dessins significatifs”.

(A. Daubree)