Complex sentence: The chapel was built of greenstone and approximately 30 ft in length and 15 ft in breadth of which only a fragment remained "in situ" and in around 1800 the chapel was converted to a fish cellar.
Split into simpler sentences: The chapel was built of greenstone and approximately 30 ft in length and 15 ft in breadth of which only a fragment remained "in situ". In around 1800 the chapel was converted to a fish cellar.