Complex sentence: The Bulbourne Valley rich in both timber and iron ore, resulted in the development of a major iron production centre by the late Pre-Roman Iron Age and the Bulbourne valley appears to have developed into a major iron production centre, of regional or national importance.
Split into simpler sentences: The Bulbourne Valley rich in both timber and iron ore, resulted in the development of a major iron production centre by the late Pre-Roman Iron Age. In the late Iron Age, the Bulbourne valley appears to have developed into a major iron production centre, of regional or national importance.