Single rock-layers may deform into for example folds. The orientation of the fols with respect to the shortening direction in pure shear is the subject of the first paragraph of this chapter. The stretch of arbitrary lines in any strain elipse is discussed in the second paragaph. Paragraphs 14-3 to 14-7 deal with the strain (history) ellipse and its meanings. Specific folds and boudinages are introduced in paragraph 8. Subjects of the three final paragraphs are equations for the rotation of material lines, surface-of-no-finite-strain and progressive deformation of competent single layers.