The branch of geology that deals with study and interpretation of deformation of the Earth's crust. Deformation brings about changes in size (dilation), shape (distortion), position (translation), or orientation (rotation). Evidence for the changes caused by deformation are commonly implanted into geologic bodies in the form of recognizable structures, such as faults and joints, folds and cleavage, and foliation and lineation. In fact, geologic structures exist because the rock bodies in which they are found were forced to undergo such changes. The geologic record of structures and structural relations is best developed and most complicated in mountain belts, the most intensely deformed parts of the Earth's crust.