The geologic record of the Proterozoic is much better than that for the preceding Archaean. In contrast to the deep-water deposits of the Archean, the Proterozoic features many strata that were laid down in extensive, shallow epicontinental seas; furthermore, many of these rocks are less metamorphosed than Archean-age ones, and plenty are in fact unaltered. Study of these rocks show that the eon featured rapid continental accretion (unique to the Proterozoic), supercontinent cycles, and mountain-building (orogeny) activity.