The deformation of layering into folds is modeled for a linear viscous medium moving over a d¿collement. Folds are generated by flow variations caused by relief on the d¿collement, variations in friction, or both. The model is applied to folds forming now in the Greenland Ice Sheet near Dye 3, for which more complete data are available than for analogous solid earth situations and for which the d¿collement is at or near the bed. The folds (wavelength 4--8 km) are detected by radio reflection sounding. Measured surface deformation and deformation rate are used with the radar results to test the theory. Calculated fold amplitude is only 20% less than that measured, which indicates that the theory is substantially correct. Inversion of the data to calculate basal drag and velocity variations is not helpful for near Dye 3 because many different basal boundary conditions can lead to the observed deformations. ¿ American Geophysical Union 1986