The frontal part of the Prebetic zone corresponds to an orogenic prism (accretionary wedge) which obeys the critical taper model. Three sections parallel to the transport direction show conspicuous similarities with the experiments performed: the southermosl section exhibit long Imbricates characteristic of high basal friction experiments and correctively the taper is wide. On the other hand the northermost section, traced in a zone where the decollement level is made up o f thick evaporitic upper Trias, shows a very narrow taper and the shortening is accommodated by decollement (detachment) folds