Complex sentence: The oldest of these flows are of Pleistocene age composed of basaltic trachyandesite and basaltic andesite, with smaller amounts of plagioclase, clinopyroxene, olivine, and hornblende.
Split into simpler sentences: The oldest of these flows are of Pleistocene age. Many of the Pleistocene age deposits are composed of basaltic trachyandesite and basaltic andesite, while containing amounts of plagioclase, clinopyroxene, olivine, and hornblende.