Complex sentence: Archean rocks in the Karelian Domain are north-south medium grade greenstone and metasedimentary belts that are intruded by granitoids and metasedimentary gneiss formed at intermediate pressures.
Split into simpler sentences: Archean rocks in the Karelian Domain are north-south medium grade greenstone and metasedimentary belts. Besides these belts and intrusions there is also metasedimentary gneiss formed at intermediate pressures.