Complex sentence: Cole pictures were produced at low cost, during either the silent era or the transitional period of the conversion to sound cinema; the vast majority of the studio's silent productions are thought to be lost, with no copies now known to exist.
Split into simpler sentences: Cole pictures were produced at low cost, during either the silent era or the transitional period of the conversion to sound cinema. The vast majority of the studio's silent productions are thought to be lost, with no copies now known to exist.