Layered structures in the vertical profiles of ozone mixing ratio as retrieved by the Stratospheric Aerosol and Gas Experiment (SAGE II) version 6.0 have been studied in the altitude range 10--28 km in the middle and high latitudes (30--75 N and S). 12 years of data (1985--1990, 1994--1999) have been used to build a climatology of layers with thickness of a few kilometers. The occurrence peaks near 12--13 km, then decreases sharply up to about 20 km before increasing again in the 20--28 km range. The seasonal variation indicates that layering activity maximizes during winter-spring in both hemispheres. This is similar to earlier results on thinner structures or laminae. A significant number of layers were observed in summer at altitudes >20 km in both hemispheres primarily at high latitudes (>60 N and S).