Rocksteady: This style is a pit stop located exactly half way on the drive from Ska to Reggae. It is not fast enough to be Ska and not slow enough to be Reggae. This tempo bridge superceded ska in 1966 and kept it’s popularity until 1968, the year that saw the birth of the even slower paced reggae, a form that continues to enthrall listeners around the globe.
from Gospelreggae.com