Complex sentence: The west coast of the lower North Island is not naturally supplied with harbours and the Foxton harbour had a dangerous bar at the river mouth but as the only real harbour between Wanganui and Wellington it was used anyway.
Split into simpler sentences: The west coast of the lower North Island is not naturally supplied with harbours and the Foxton harbour had a dangerous bar at the river mouth. As the only real harbour between Wanganui and Wellington it was used anyway.