Complex sentence: Among Segerstam's juvenilia from 1960--1969, are four string quartets from 1962--1966, and the post-impressionist ballet "Pandora" from 1967, which are usually labeled as being from his "Post-Expressionist" period.
Split into simpler sentences: Among Segerstam's juvenilia (1960--1969) are four string quartets from 1962--1966, and the post-impressionist ballet "Pandora" from 1967. The quartets are usually labeled as being from his "Post-Expressionist" period.