Determining finite strain: how far have we progressed?

One of the main aims in the field of structural geology is the identification and quantification of deformation or strain. This pursuit has occupied geologists since the 1800s, but has evolved dramatically since those early studies. The quantification of strain in sedimentary lithologies was initially restricted to lithologies of known initial shape, such as fossils or reduction spots. In 1967, Ramsay presented a series of methods and calculations, which allowed populations of clasts to be used as strain markers. These methods acted as a foundation for modern strain analysis, and have influenced thousands of studies. This review highlights the significance of Ramsay's contribution to modern strain analysis. We outline the advances in the field over the 50 years since publication of Folding and Fracturing of Rocks, review the existing limitations of strain analysis methods and look to future developments.