Folding in rocks is very common, yet is still imperfectly understood. Very slow natural strain rates and development of large strains over extremely long times make direct laboratory modeling impossible. Theoretical treatment only adequately account for initial stages of folding. This research will attempt to circumvent these problems by using a two-dimensional finite- element model with appropriate choice of constitutive relation- ships to study development of folds with time. Predictions of shape and strain distribution resulting from the model will then be compared with data on natural folds. The aim is to provide criteria for gaining information from natural folds about deformational history and about rheology of rocks deformed under slow natural conditions.