ABSTRACT
This chapter deals with the arrangements of sedimentary rocks as structural units in the Earth’s outer crust and describes the basic geological structures. Strike and dip are two fundamental conceptions in structural geology, and are the geologist’s method of defining the attitude of inclined strata. The formation of folds has in many cases been due to the operation of forces tangential to the Earth’s surface; the rocks have responded to crustal compression by bending or buckling, to form a fold-system whose pattern is related to the controlling forces. Flow-folding is an example of incompetent behaviour and arises in beds which offer little resistance to deformation, such as salt deposits, or rocks which become ductile when buried at considerable depth in the crust where high temperatures prevail, as for some gneisses. The relative strength of strata during folding is reflected by the relationship between folds.
