Complex sentence: Upon reaching the river, Olvir flees through the mountains, and is last heard making for the "Suðreyjar"; he is not mentioned again within the "Orkneyinga saga".
Split into simpler sentences: Upon reaching the river, Olvir flees through the mountains, and is last heard making for the "Suðreyjar". He is not mentioned again within the "Orkneyinga saga".