Complex sentence: The remains consist of an octagonal concrete base that measure 3850mm across with a channel running west to east across the middle on the southern edge of the octagon is a raised area of concrete which is 225mm higher than the rest of the base.
Split into simpler sentences: The remains consist of an octagonal concrete base that measure 3850mm across with a channel running west to east across the middle. On the southern edge of the octagon is a raised area of concrete which is 225mm higher than the rest of the base.